Problem p02573 (python)

Fixed submission:
from collections import Counter 

class UnionFind(object):
    def __init__(self, n=1):
        self.par = [i for i in range(n)]
        self.rank = [0 for _ in range(n)]

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

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x != y:
            if self.rank[x] < self.rank[y]:
                x, y = y, x
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1
            self.par[y] = x

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

N,M= map(int, input().split())
uf1=UnionFind(N)

for _ in range(M):
    x, y = map(int, input().split())
    uf1.union(x-1,y-1)

for i in range(N):
    uf1.find(i) 
c = list(Counter(uf1.par).values())
print(max(c))

Buggy submission (verdict: Runtime Error):
N, M = map(int, input().split())
UF = [-1] * (N+1)
def find(x):
    global UF
    if UF[x] == -1:
        return x
    else:
        UF[x] = find(UF[x])
        return UF[x]
def union(x,y):
    global UF
    xx = find(x)
    yy = find(y)
    if UF[x] == UF[y] == -1:
        UF[y] = xx
        return
    elif xx == yy:
        return 
    else:
        UF[yy] = xx
        return 
    
for _ in range(M):
    x, y = map(int, input().split())
    union(x,y)
    
cnt = [0] * (N+1)
for i in range(1,N+1):
    z = find(i)
    cnt[z] += 1

print(max(cnt))

Buggy submission (verdict: Runtime Error):
import sys
sys.setrecursionlimit(10*100)

N, M = map(int, input().split())
UF = [-1] * (N+1)
def find(x):
    global UF
    if UF[x] == -1:
        return x
    else:
        UF[x] = find(UF[x])
        return UF[x]
def union(x,y):
    global UF
    xx = find(x)
    yy = find(y)
    if UF[x] == UF[y] == -1:
        UF[y] = xx
        return
    elif xx == yy:
        return 
    else:
        UF[yy] = xx
        return 
    
for _ in range(M):
    x, y = map(int, input().split())
    union(x,y)
    
cnt = [0] * (N+1)

for i in range(1,N+1):
    z = find(i)
    cnt[z] += 1

print(max(cnt))

Buggy submission (verdict: Runtime Error):
N, M = map(int, input().split())
UF = [-1] * (N+1)
def find(x):
    global UF
    if UF[x] == -1:
        return x
    else:
        UF[x] = find(UF[x])
        return UF[x]
def union(x,y):
    global UF
    xx = find(x)
    yy = find(y)
    if UF[x] == UF[y] == -1:
        UF[y] = xx
        return
    elif xx == yy:
        return 
    else:
        UF[yy] = xx
        return 
    
for _ in range(M):
    x, y = map(int, input().split())
    union(x,y)
    
cnt = [0] * (N+1)

for i in range(1,N+1):
    z = find(i)
    cnt[z] += 1

print(max(cnt))

Buggy submission (verdict: Runtime Error):
N, M = map(int, input().split())
UF = [-1] * (N+1)
def find(x):
    global UF
    if UF[x] == -1:
        return x
    else:
        UF[x] = find(UF[x])
        return UF[x]
def union(x,y):
    global UF
    xx = find(x)
    yy = find(y)
    if UF[x] == UF[y] == -1:
        UF[y] = xx
        return
    elif xx == yy:
        return 
    else:
        UF[yy] = xx
        return 
    
for _ in range(M):
    x, y = map(int, input().split())
    union(x,y)
    
cnt = [0] * (N+1)

for i in range(1,N+1):
    z = find(i)
    if z == -1:
        continue
    cnt[z] += 1

print(max(cnt))