Problem p02787 (python)

Fixed submission:
# coding: utf-8
import re
import math
import fractions
import random
from heapq import heappop,heappush
import time
import sys
readline = sys.stdin.readline
#import numpy as np
mod=int(10**9+7)
inf=int(10**20)
class union_find():
    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 bin_(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 comb(n,r):return math.factorial(n)//math.factorial(n-r)//math.factorial(r)
def next_comb(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
 

 
#main
h,n=map(int,input().split())
AB=[list(map(int,input().split())) for a in range(n)]
dp=[[inf for b in range(h+1)] for a in range(n+1)]
dp[0][0]=0

for a in range(1,n+1):
    for b in range(0,h+1):
        dp[a][b]=min(dp[a][b],dp[a-1][b])
        key=min(h,b+AB[a-1][0])
        dp[a][key]=min(dp[a][key],dp[a][b]+AB[a-1][1])
print(dp[n][h])

Buggy submission (verdict: Runtime Error):
# coding: utf-8
import re
import math
import fractions
import random
from heapq import heappop,heappush
import time
import sys
readline = sys.stdin.readline
#import numpy as np
mod=int(10**9+7)
inf=int(10**20)
class union_find():
    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 bin_(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 comb(n,r):return math.factorial(n)//math.factorial(n-r)//math.factorial(r)
def next_comb(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
 

 
#main
h,n=map(int,input().split())
AB=[list(map(int,input().split())) for a in range(n)]
dp=[[inf for b in range(h+1)] for a in range(n+1)]
dp[0][0]=0

for a in range(1,n+1):
    for b in range(0,h+1):
        key=min(h,b+AB[a-1][0])
        dp[key]=min(dp[key],dp[b]+AB[a-1][1])
print(dp[n][h])

Buggy submission (verdict: Runtime Error):
# coding: utf-8
import re
import math
import fractions
import random
from heapq import heappop,heappush
import time
import sys
readline = sys.stdin.readline
#import numpy as np
mod=int(10**9+7)
inf=int(10**20)
class union_find():
    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 bin_(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 comb(n,r):return math.factorial(n)//math.factorial(n-r)//math.factorial(r)
def next_comb(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
 

 
#main
h,n=map(int,input().split())
AB=[list(map(int,input().split())) for a in range(n)]
dp=[[inf for b in range(h+1)] for a in range(n+1)]
dp[0][0]=0

for a in range(1,n+1):
    for b in range(0,h+1):
        dp[a][b]=min(dp[a][b],dp[a-1][b])
        key=min(h,b+AB[a-1][0])
        dp[a][key]=min(dp[a][key],dp[a][b]+AB[a-1][1])
print(min(dp[n][h]))