Problem:


Score : 300 points

Problem Statement

There are N cities numbered 1 through N, and M bidirectional roads numbered 1 through M.
Road i connects City A_i and City B_i.

Snuke can perform the following operation zero or more times:

Choose two distinct cities that are not directly connected by a road, and build a new road between the two cities.

After he finishes the operations, it must be possible to travel from any city to any other cities by following roads (possibly multiple times).

What is the minimum number of roads he must build to achieve the goal?

Constraints

2 \leq N \leq 100,000

1 \leq M \leq 100,000

1 \leq A_i < B_i \leq N

No two roads connect the same pair of cities.

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N M
A_1 B_1
:
A_M B_M

Output

Print the answer.

Sample Input 1

3 1
1 2

Sample Output 1

1

Initially, there are three cities, and there is a road between City 1 and City 2.

Snuke can achieve the goal by building one new road, for example, between City 1 and City 3.
After that,

We can travel between 1 and 2 directly.

We can travel between 1 and 3 directly.

We can travel between 2 and 3 by following both roads (2 - 1 - 3).



Sample input:
3 1
1 2


Sample output:
1

Submission status: Accepted

Solution code:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)


n, m = map(int, input().split())
uf = UnionFind(n)
for i in range(m):
    a, b = map(int, input().split())
    a -= 1
    b -= 1
    uf.union(a, b)

s = set([])
for i in range(n):
    s.add(uf.find(i))

print(len(s)-1)

Submission status: Accepted

Solution code:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())


N, M = [int(i) for i in input().split()]
ABS = [[int(i) for i in input().split()] for _ in range(M)]

uf = UnionFind(N+1)
for a, b in ABS:
  uf.union(a, b)

print(uf.group_count() - 2)

Submission status: Accepted

Solution code:
# coding: utf-8
#import numpy as np
import re
import math
from collections import defaultdict,deque,Counter
from fractions import Fraction
import bisect
import itertools
from itertools import accumulate
from copy import deepcopy

import heapq
import random
import time
import os
import sys
from functools import lru_cache,reduce
readline=sys.stdin.readline
sys.setrecursionlimit(100000)
alp="abcdefghijklmnopqrstuvwxyz"
numbers="0123456789"
mod=int(10**9+7)
inf=int(10**19)
class Set():
    def __init__(self,A=[]):
        self.heap=[]
        self.dic=defaultdict(bool)
        self.size=0
        for a in A:self.add(a)
    
    def __str__(self):
        return str(self.heap)
    
    def add(self,x):
        if not self.find(x):
            heapq.heappush(self.heap,x)
            self.dic[x]=True
            self.size+=1

    def remove(self,x):
        if self.find(x):
            self.dic[x]=False
            self.size-=1

    def find(self,x):
        return self.dic[x]
    
    def top(self):
        while self.heap and self.dic[self.heap[0]]==False:
            heapq.heappop(self.heap)
        if self.heap:return self.heap[0]
        else:return None

    def pop(self):
        ret=None
        if self.heap:
            ret=self.top()
            self.remove(ret)
        return ret
class multiset():
    def __init__(self,A=[]):
        self.heap=[]
        self.dic=defaultdict(int)
        self.size=0
        for a in A:self.add(a)
    
    def __str__(self):
        return str(self.heap)
    
    def add(self,x):
        heapq.heappush(self.heap,x)
        self.dic[x]+=1
        self.size+=1

    def remove(self,x):
        if self.dic[x]>0:
            self.dic[x]-=1
            self.size-=1
    
    def count(self,x):
        return self.dic[x]

    def find(self,x):
        return self.dic[x]>0
    
    def top(self):
        while self.heap and self.dic[self.heap[0]]==0:
            heapq.heappop(self.heap)
        if self.heap:return self.heap[0]
        else:return None

    def pop(self):
        ret=None
        if self.heap:
            ret=self.top()
            self.remove(ret)
        return ret
class Edge():
    def __init__(self,x,y,val=1):
        self.x=x
        self.y=y
        self.val=val
class Point():
    def __init__(self,y,x):
        self.x=x
        self.y=y
class unionfind():
    def __init__(self,n):
        self.n=n
        self.P=[a for a in range(n)]
        self.rank=[0]*n
 
    def find(self,x):
        if(x!=self.P[x]):
            self.P[x]=self.find(self.P[x])
        return self.P[x]
 
    def same(self,x,y):
        return self.find(x)==self.find(y)
 
    def link(self,x,y):
        if self.rank[x]<self.rank[y]:
            self.P[x]=y
        elif self.rank[y]<self.rank[x]:
            self.P[y]=x
        else:
            self.P[x]=y
            self.rank[y]+=1
 
    def unite(self,x,y):
        self.link(self.find(x),self.find(y))
 
    def size(self):
        S=set()
        for a in range(self.n):
            S.add(self.find(a))
        return len(S)
def yn(b):print("yes" if b else "no")
def Yn(b):print("Yes" if b else "No")
def YN(b):print("YES" if b else "NO")
def ispow(a,b):
    now=b
    while now<a:
        now*=b
    return now==a
def getbin(num,size):
    A=[0]*size
    for a in range(size):
        if (num>>(size-a-1))&1==1:
            A[a]=1
        else:
            A[a]=0
    return A
def getfacs(n,mod_=0):
    A=[1]*(n+1)
    for a in range(2,len(A)):
        A[a]=A[a-1]*a
        if(mod_>0):A[a]%=mod_
    return A
def comb(n,r,mod,fac):
    if(n-r<0):return 0
    return (fac[n]*pow(fac[n-r],mod-2,mod)*pow(fac[r],mod-2,mod))%mod
def nextcomb(num,size):
    x=num&(-num)
    y=num+x
    z=num&(~y)
    z//=x
    z=z>>1
    num=(y|z)
    if(num>=(1<<size)):return False
    else:return num
def getprimes(n):
    if n==0:return []
    A=[True]*(n+1)
    A[0]=False
    A[1]=False
    for a in range(2,n+1):
        if A[a]:
            for b in range(a*2,n+1,a):
                A[b]=False
    ret=[]
    for a in range(n+1):
        if(A[a]):ret.append(a)
    return ret
def isprime(num):
    if(num<=1):return False
    i=2
    while i*i<=num:
       if(num%i==0):return False
       i+=1
    return True
def ifelse(b,t,f):return t if b else f
def factorize(n):
    b = 2
    ret=defaultdict(int)
    while b * b <= n:
        while n % b == 0:
            n //= b
            ret[b]+=1
        b+=1
    if n > 1:ret[n]+=1
    return ret
def inputintlist(row=1): 
    if row==1:
        ret=list(map(int,input().split()))
    else:
        ret=[None]*row
        for a in range(row):
            ret[a]=int(input())
    return ret
def inputfloatlist(row=1): 
    if row==1:
        ret=list(map(float,input().split()))
    else:
        ret=[None]*row
        for a in range(row):
            ret[a]=float(input())
    return ret
def istanchouzouka(A):
    f=True
    prev=min(A)-1
    for a in A:
        if prev>=a:
            f=False
        prev=a
    return f
def istanchouhigensyou(A):
    f=True
    prev=min(A)-1
    for a in A:
        if prev>a:
            f=False
        prev=a
    return f
def getallsum(A):
    s=sum(A)
    dp=defaultdict(int)
    dp[0]=1
    for a in range(0,len(A)):
        for b in range(s,-1,-1):
            if b-A[a]>=0:
                dp[b]+=dp[b-A[a]]
    return dp
def yuukoutomukou(edges):
    ret=deepcopy(edges)
    for edge in edges:
        if not edge.x==edge.y:
            ret.append(Edge(edge.y,edge.x,edge.val))
    return ret
def dijkstra(edges,V,start):
    from queue import PriorityQueue
    mincost=[inf]*V
    G=[[] for a in range(V)]
    for edge in edges:
        G[edge.x].append([edge.val,edge.y])
    Q=PriorityQueue()
    Q.put([0,start])#[cost,x]
    while not Q.empty():
        nowcost,nowx=Q.get()
        if mincost[nowx]==inf:
            mincost[nowx]=nowcost
            for cost,y in G[nowx]:
                newcost=nowcost+cost
                Q.put([newcost,y])
    return mincost
def warshallfloyd(edges,V):
    mincost=[[inf for b in range(V)] for a in range(V)]
    for a in range(V):mincost[a][a]=0
    for edge in edges:
        mincost[edge.x][edge.y]=min(mincost[edge.x][edge.y],edge.val)#x→yが複数ある場合のためにmin()する
    for k in range(V):
        for s in range(V):
            for t in range(V):
                if mincost[s][k]==inf or mincost[k][t]==inf:continue
                mincost[s][t]=min(mincost[s][t],mincost[s][k]+mincost[k][t])
    return mincost
def bellemanford(edges,V,start):
    mincost=[inf]*V
    mincost[start]=0
    for _ in range(V):
        for edge in edges:
            if mincost[edge.x]==inf:continue
            mincost[edge.y]=min(mincost[edge.y],mincost[edge.x]+edge.val)
    return mincost
def getmd(x1,y1,x2,y2):return abs(x1-x2)+abs(y1-y2)
def geted(x1,y1,x2,y2):return math.sqrt((x1-x2)**2+(y1-y2)**2)
class fordfulkerson():
    def __init__(self,edges,V,s,t):
        self.V=V
        self.used=[False]*V
        self.G=[[] for a in range(V)]
        self.s=s
        self.t=t
        for edge in edges:
            self.G[edge.x].append({"x":edge.x,"y":edge.y,"cap":edge.val,"rev":len(self.G[edge.y])})
            self.G[edge.y].append({"x":edge.y,"y":edge.x,"cap":0,"rev":len(self.G[edge.x])-1})
    def dfs(self,v,t,f=inf):
        if v==t:return f
        self.used[v]=True
        for a in range(len(self.G[v])):
            x=self.G[v][a]["x"]
            y=self.G[v][a]["y"]
            cap=self.G[v][a]["cap"]
            rev=self.G[y][self.G[x][a]["rev"]]
            if self.used[y] or cap==0:continue
            f2=self.dfs(y,t,min(f,cap))
            if f2>0:
                self.G[v][a]["cap"]-=f2
                rev["cap"]+=f2
                return f2
        return 0
    def maxflow(self):
        flow=0
        while True:
            self.used=[False]*V
            zouka=self.dfs(self.s,self.t)
            if zouka==0:break
            flow+=zouka
        return flow
def zipsort(*args):
    ziplist=sorted(zip(*args))
    for a in range(len(args)):
        for b in range(len(ziplist)):
            args[a][b]=ziplist[b][a]
def zipreverse(*args):
    ziplist=list(zip(*args))
    rev=[]
    for a in range(len(ziplist)-1,-1,-1):
        rev.append(ziplist[a])
    for a in range(len(args)):
        for b in range(len(rev)):
            args[a][b]=rev[b][a]

def to10(A):
    ret=0
    for a in range(len(A)-1,-1,-1):
        ret+=X[a]*2**(N-1-a)
    return ret
######################################################################################################
N,M=inputintlist()
U=unionfind(N)
for a in range(M):
    A,B=inputintlist()
    A-=1
    B-=1
    U.unite(A,B)
s=set()
for a in range(N):
    s.add(U.find(a))
ans=len(s)-1
print(ans)

Submission status: Accepted

Solution code:
N, M = map(int, input().split())

class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())
      
uf = UnionFind(N+1)

for m in range(M):
  a, b = map(int, input().split())
  uf.union(a, b)
  
print(len(uf.roots()) - 1 - 1)

Submission status: Accepted

Solution code:
class UnionFind:
    def __init__(self, n):
        self.par = [i for i in range(n+1)]
        self.rank = [0] * (n+1)
        self.num = [1] * (n+1)#集合の要素の数
 
    # 検索
    def find(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]
 
    # 併合
    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if self.rank[x] < self.rank[y]:
            self.par[x] = y
            self.num[y]+=self.num[x]
        else:
            self.par[y] = x
            self.num[x]+=self.num[y]
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1
 
    # 同じ集合に属するか判定
    def same_check(self, x, y):
        return self.find(x) == self.find(y)
n, m = map(int, input().split())
uf = UnionFind(n)
for i in range(m):
  a, b = map(int, input().split())
  uf.union(a,b)
  
ans = 0
for i in range(1, n+1):
  if uf.par[i]==i:
    ans+=1
print(ans-1)

Submission status: Accepted

Solution code:
import sys
from scipy.sparse.csgraph import connected_components
from scipy.sparse import csr_matrix

input = sys.stdin.buffer.readline
int1 = lambda x: int(x) - 1

N, M = map(int, input().split())
frm, to = [], []
for _ in range(M):
    a, b = map(int1, input().split())
    frm.append(a)
    to.append(b)

matr = csr_matrix(([1] * M, (frm, to)), shape=(N, N))
p, _ = connected_components(matr)
print(p - 1)

Submission status: Accepted

Solution code:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

N, M = map(int, input().split())
uf = UnionFind(N)

for i in range (0, M):
    A, B = map(int, input().split())
    uf.union(A-1, B-1)

print(uf.group_count()-1)

Submission status: Accepted

Solution code:
import sys
import bisect
from functools import lru_cache
from collections import defaultdict
inf = float('inf')
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(10**6)
def input(): return sys.stdin.readline().rstrip()
def read():
  return int(readline())
def reads():
  return map(int, readline().split())

N,M=reads()

    
class UnionFind():
    def __init__(self, n):
        self.n=n
        self.parents=[-1]*n # 親(uf.find()で経路圧縮して根)の番号。根の場合は-(そのグループの要素数)
    def find(self,x):
        #グループの根を返す
        if self.parents[x]<0:return x
        else:
            self.parents[x]=self.find(self.parents[x])
            return self.parents[x]
    #def members(self, x):
    #    root = self.find(x)
    #    return [i for i in range(self.n) if self.find(i) == root]
    def unite(self,x,y):
        #要素x,yのグループを併合
        x,y=self.find(x),self.find(y)
        if x==y:return
        if self.parents[x]>self.parents[y]:#要素数の大きい方をxに
            x,y=y,x
        self.parents[x]+=self.parents[y]
        self.parents[y]=x #要素数が大きい方に併合
    def roots(self):
        #全ての根の要素のリスト
        return [i for i, x in enumerate(self.parents) if x<0]
    def group_count(self):
        #グループの数
        return len(self.roots())
    #def __str__(self):
    #   return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

uf=UnionFind(N)
for i in range(M):
    a,b=reads()
    uf.unite(a-1,b-1)
count=uf.group_count()
print(count-1)

Submission status: Accepted

Solution code:
import sys

sys.setrecursionlimit(10 ** 8)


def union(x, y):
    x = find(x)
    y = find(y)
    if x == y:
        return
    parent[x] = y


def find(x):
    if parent[x] == -1:
        return x
    res = parent[x] = find(parent[x])
    return res




N, M = map(int, input().split())
parent = [-1] * N
for _ in range(M):
    A, B = map(int, input().split())
    union(A - 1, B - 1)

groups = set()
for i in range(N):
    groups.add(find(i))
print(len(groups) - 1)

Submission status: Accepted

Solution code:
#!/usr/bin/env python3
import sys
input = sys.stdin.readline

class DisjointSet:
    def __init__(self, n):
        self.par = [i for i in range(n)]
        self.size = [1] * n
        self.rank = [0] * n

    def root(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.root(self.par[x])
            return self.par[x]

    def has_same_root(self, x, y):
        return self.root(x) == self.root(y)

    def get_size(self, x):
        return self.size[self.root(x)]

    def unite(self, x, y):
        x = self.root(x)
        y = self.root(y)
        if x == y:
            return
        if self.rank[x] < self.rank[y]:
            self.par[x] = y
            self.size[y] += self.size[x] 
        else:
            self.par[y] = x
            self.size[x] += self.size[y]
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1


n, m = map(int, input().split())
DS = DisjointSet(n)
for _ in range(m):
    a, b = map(int, input().split())
    a -= 1; b -= 1
    DS.unite(a, b)
seen = set()
ans = 0
for i in range(n):
    r = DS.root(i)
    if r in seen:
        continue
    else:
        seen.add(r)
        ans += 1
print(ans - 1)

Submission status: Accepted

Solution code:
# coding:UTF-8
import sys
from math import factorial

MOD = 10 ** 9 + 7
INF = float('inf')

# ユニオンファインド木
class UnionFind:
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n
        self.rank = [0] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return
        elif self.rank[x] > self.rank[y]:
            self.parents[x] += self.parents[y]
            self.parents[y] = x
        else:
            self.parents[y] += self.parents[x]
            self.parents[x] = y
            if self.rank[x] == self.rank[y]:
                self.rank[y] += 1

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

N, M = list(map(int, input().split()))     # スペース区切り連続数字
AB = [list(map(int, input().split())) for _ in range(M)]     # スペース区切り連続数字(行列)

un = UnionFind(N)
for a, b in AB:
    un.union(a-1, b-1)

g = len(un.roots())

print("{}".format(g-1))

Submission status: Accepted

Solution code:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())
      
n,m=map(int,input().split())
uf=UnionFind(n)
for i in range(m):
  a,b=map(int,input().split())
  a-=1
  b-=1
  uf.union(a,b)
print(uf.group_count()-1)

Submission status: Accepted

Solution code:
#UnionFind
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())
    
n,m = map(int,input().split())
uf = UnionFind(n+1)
for _ in range(m):
    a,b = map(int,input().split())
    uf.union(a,b)

print(uf.group_count()-2)

Submission status: Accepted

Solution code:
import sys
# sys.setrecursionlimit(100000)


class UnionFind:
    def __init__(self, n: int):
        self.nodes = n
        self.parents = [-1] * n
        self.rank = [0] * n

    # retrun the root of element x
    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    # unite the group include element x and group include element y
    def unite(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return
        if self.rank[x] < self.rank[y]:
            self.parents[y] += self.parents[x]
            self.parents[x] = y
        else:
            self.parents[x] += self.parents[y]
            self.parents[y] = x
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1

    # get size of the gourp which element x belongs
    def get_size(self, x):
        return -self.parents[self.find(x)]

    # check if element x and element y is same group
    def same(self, x, y):
        return self.find(x) == self.find(y)


def input():
    return sys.stdin.readline().strip()


def input_int():
    return int(input())


def input_int_list():
    return [int(i) for i in input().split()]


def main():
    n, m = input_int_list()
    union = UnionFind(n)
    for _ in range(m):
        a, b = input_int_list()
        # 0-indexed
        a -= 1
        b -= 1
        union.unite(a, b)
    cnt = 0
    for p in union.parents:
        if p < 0:
            cnt += 1
    print(cnt - 1)

    return


if __name__ == "__main__":
    main()

Submission status: Accepted

Solution code:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents =[-1 for i in range(n)]
    # どのグループに属しているかを返す
    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def unite(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return False
        if self.parents[x] > self.parents[y]:
            x, y = y, x
        self.parents[x] += self.parents[y]
        self.parents[y] = x
        return True

    def size(self, x):
        return -self.parents[self.find(x)]

N, M = map(int, input().split())
ut = UnionFind(N)
for i in range(M):
    x, y = list(map(int, input().split()))
    ut.unite(x-1, y-1)
ans = -1
for x in ut.parents:
    if x < 0:
        ans += 1
print(ans)

Submission status: Accepted

Solution code:
#C
class UnionFind():
    # https://www.slideshare.net/chokudai/union-find-49066733
    # 作りたい要素数nで初期化
    # 使用するインスタンス変数の初期化
    def __init__(self, n):
        self.n = n
        # root[x]<0ならそのノードが根かつその値が木の要素数
        # rootノードでその木の要素数を記録する
        # root[x]>=0の場合は、特に直接的な意味を持たない気がする。計算に寄与するので意味はあるのだろうが。
        self.root = [-1]*(n+1)
        # 木をくっつける時にアンバランスにならないように調整する
        # 無結合の時はRank=0,結合して1つ木が深くなると根がRank+=1
        self.rnk = [0]*(n+1)

    # ノードxのrootノードを見つける
    #
    def Find_Root(self, x):
        if(self.root[x] < 0):
            return x
        else:
            # ここで代入しておくことで、後の繰り返しを避ける
            self.root[x] = self.Find_Root(self.root[x])
            return self.root[x]

    # 木の併合、入力は併合したい各ノード
    def Unite(self, x, y):
        # 入力ノードのrootノードを見つける
        x = self.Find_Root(x)
        y = self.Find_Root(y)
        # すでに同じ木に属していた場合
        if(x == y):
            return
        # 違う木に属していた場合rnkを見てくっつける方を決める
        # (1)xのランクの方が大きい(位置が深い)場合
        elif(self.rnk[x] > self.rnk[y]):
            self.root[x] += self.root[y]
            self.root[y] = x

        # (2)yのランクの方が大きい(位置が深い)場合 or 等しい場合
        # また等しい場合、引数の2つめのyの方のランクを1つ増やす
        else:
            self.root[y] += self.root[x]
            self.root[x] = y
            # rnkが同じ（深さに差がない場合）は1増やす
            if(self.rnk[x] == self.rnk[y]):
                self.rnk[y] += 1

    # xとyが同じグループに属するか判断
    # Return: True or False
    def isSameGroup(self, x, y):
        return self.Find_Root(x) == self.Find_Root(y)

    # ノードxが属する木のサイズを返す
    def Count(self, x):
        return -self.root[self.Find_Root(x)]
    
#####################################################################    
N,M = map(int,input().split())
UN=UnionFind(N)
A=[0]*M
B=[0]*M
for i in range(M):
    A[i],B[i] = map(int,input().split())
    UN.Unite(A[i],B[i])

#print(UN.root)
cnt=0
for i in range(1,N+1):
    if UN.root[i]<0:
        cnt +=1
print(cnt-1)

Submission status: Accepted

Solution code:
class UnionFind():
# ***0-based index!!!***
    def __init__(self, n):
        self.n = n
        self.parent = [-1 for i in range(n)]
    
    def root(self, x):
        if self.parent[x] <0:
            return x
        else:
            self.parent[x] = self.root(self.parent[x])
            return self.parent[x]
    
    def same(self, x, y):
        return (self.root(x) == self.root(y))

    def union(self, x, y):
        p = self.root(x)
        q = self.root(y)
        
        if not p==q :
            if self.parent[p] > self.parent[q]:
                p,q = q,p
            self.parent[p] += self.parent[q]
            self.parent[q] = p
    
    def size(self, x):
        return -self.parent[self.root(x)]


N,M = list(map(int, input().split()))
uf = UnionFind(N)
for i in range(M):
    A,B = list(map(int, input().split()))
    uf.union(A-1, B-1)

ans = 0
for i in range(N):
    if uf.root(i) == i:
        ans += 1
print(ans-1)

Submission status: Accepted

Solution code:
from collections import deque
N,M = map(int,input().split())
G = {i:[] for i in range(1,N+1)}
for _ in range(M):
    a,b = map(int,input().split())
    G[a].append(b)
    G[b].append(a)
col = [-1 for _ in range(N+1)]
cnt = 0
for i in range(1,N+1):
    if col[i]<0:
        col[i] = cnt
        que = deque([i])
        while que:
            x = que.popleft()
            for y in G[x]:
                if col[y]<0:
                    col[y]=cnt
                    que.append(y)
        cnt += 1
cmax = max(col)
print(cmax)

Submission status: Accepted

Solution code:

class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

N,M=map(int,input().split())
tree=UnionFind(N)
for i in range(M):
  A,B=map(int,input().split())
  tree.union(A-1,B-1)
print(tree.group_count()-1)