Buggy python submission (verdict: Time Limit Exceeded):
ii = lambda : int(input())
mi = lambda : map(int,input().split())
li = lambda : list(map(int,input().split()))

def main():
    n,m = mi()
    tree = [set() for _ in range(n)]
    for i in range(m):
        s,t = mi()
        tree[s-1].add(t-1)
    dp = [0]*n
    dpl = [0]*n
    for i in range(n-1):
        dpl[i] = len(tree[i])
    for i in reversed(range(n-1)):
        for k in tree[i]:
            dp[i] += dp[k] 
        dp[i] /= dpl[i]
        dp[i] += 1
    ans = dp[0]
    
    def func(ss,tt):
        tmp = 0
        for l in tree[ss]:
            if l == tt:
                continue
            tmp += dp[l]
        tmp = tmp/(dpl[ss] -1) + 1
        if tmp > dp[ss]:
            return dp[0]
        else:
            dp[ss] = tmp
        
        for a in reversed(range(ss)):
            tmp = 0
            for b in tree[a]:
                tmp += dp[b]
            dp[a] = tmp/dpl[a] + 1
        
        return dp[0]
    
    for i in range(n-1):
        if len(tree[i]) == 1:
            continue
        for k in tree[i]:
            ans = min(ans,func(i,k))
    print(ans)

main()

Fixed submission:
ii = lambda : int(input())
mi = lambda : map(int,input().split())
li = lambda : list(map(int,input().split()))

n,m = mi()
tree = [[] for _ in range(n)]
for i in range(m):
    s,t = mi()
    tree[s-1].append(t-1)
dp = [0]*n
for i in reversed(range(n-1)):
    size = len(tree[i])
    for k in tree[i]:
        dp[i] += dp[k] 
    dp[i] /= size
    dp[i] += 1
ans = dp[0]

def func(ss,tt):
    tmp = 0
    for l in tree[ss]:
        if l == tt:
            continue
        tmp += dp[l]
    tmp = tmp/(len(tree[ss])-1) + 1
    if tmp > dp[ss]:
        return dp[0]
    else:
        dp[ss] = tmp
    
    for a in reversed(range(ss)):
        tmp = 0
        for b in tree[a]:
            tmp += dp[b]
        dp[a] = tmp/len(tree[a]) + 1
    
    return dp[0]

for i in range(n-1):
    if len(tree[i]) == 1:
        continue
    for k in tree[i]:
        ans = min(ans,func(i,k))
print(ans)

Buggy python submission (verdict: Runtime Error):
ii = lambda : int(input())
mi = lambda : map(int,input().split())
li = lambda : list(map(int,input().split()))

def main():
    n,m = mi()
    tree = [set() for _ in range(n)]
    for i in range(m):
        s,t = mi()
        tree[s-1].append(t-1)
    dp = [0]*n
    dpl = [0]*n
    for i in range(n-1):
        dpl[i] = len(tree[i])
    for i in reversed(range(n-1)):
        for k in tree[i]:
            dp[i] += dp[k] 
        dp[i] /= dpl[i]
        dp[i] += 1
    ans = dp[0]
    
    def func(ss,tt):
        tmp = 0
        for l in tree[ss]:
            if l == tt:
                continue
            tmp += dp[l]
        tmp = tmp/(dpl[ss] -1) + 1
        if tmp > dp[ss]:
            return dp[0]
        else:
            dp[ss] = tmp
        
        for a in reversed(range(ss)):
            tmp = 0
            for b in tree[a]:
                tmp += dp[b]
            dp[a] = tmp/dpl[a] + 1
        
        return dp[0]
    
    for i in range(n-1):
        if len(tree[i]) == 1:
            continue
        for k in tree[i]:
            ans = min(ans,func(i,k))
    print(ans)

main()

Fixed submission:
ii = lambda : int(input())
mi = lambda : map(int,input().split())
li = lambda : list(map(int,input().split()))

n,m = mi()
tree = [[] for _ in range(n)]
for i in range(m):
    s,t = mi()
    tree[s-1].append(t-1)
dp = [0]*n
for i in reversed(range(n-1)):
    size = len(tree[i])
    for k in tree[i]:
        dp[i] += dp[k] 
    dp[i] /= size
    dp[i] += 1
ans = dp[0]

def func(ss,tt):
    tmp = 0
    for l in tree[ss]:
        if l == tt:
            continue
        tmp += dp[l]
    tmp = tmp/(len(tree[ss])-1) + 1
    if tmp > dp[ss]:
        return dp[0]
    else:
        dp[ss] = tmp
    
    for a in reversed(range(ss)):
        tmp = 0
        for b in tree[a]:
            tmp += dp[b]
        dp[a] = tmp/len(tree[a]) + 1
    
    return dp[0]

for i in range(n-1):
    if len(tree[i]) == 1:
        continue
    for k in tree[i]:
        ans = min(ans,func(i,k))
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
ii = lambda : int(input())
mi = lambda : map(int,input().split())
li = lambda : list(map(int,input().split()))

n,m = mi()
tree = [[] for _ in range(n)]
for i in range(m):
    s,t = mi()
    tree[s-1].append(t-1)
dp = [0]*n
for i in reversed(range(n-1)):
    size = len(tree[i])
    for k in tree[i]:
        dp[i] += dp[k] 
    dp[i] /= size
    dp[i] += 1
ans = dp[0]

def func(ss,tt):
    tmp = 0
    for l in tree[ss]:
        if l == tt:
            continue
        tmp += dp[l]
    dp[ss] = tmp/(len(tree[ss])-1) + 1
    
    for a in reversed(range(ss)):
        tmp = 0
        for b in tree[a]:
            tmp += dp[b]
        dp[a] = tmp/len(tree[a]) + 1
    
    return dp[0]

for i in range(n-1):
    if len(tree[i]) == 1:
        continue
    for k in tree[i]:
        ans = min(ans,func(i,k))
print(ans)



Fixed submission:
ii = lambda : int(input())
mi = lambda : map(int,input().split())
li = lambda : list(map(int,input().split()))

n,m = mi()
tree = [[] for _ in range(n)]
for i in range(m):
    s,t = mi()
    tree[s-1].append(t-1)
dp = [0]*n
for i in reversed(range(n-1)):
    size = len(tree[i])
    for k in tree[i]:
        dp[i] += dp[k] 
    dp[i] /= size
    dp[i] += 1
ans = dp[0]

def func(ss,tt):
    tmp = 0
    for l in tree[ss]:
        if l == tt:
            continue
        tmp += dp[l]
    tmp = tmp/(len(tree[ss])-1) + 1
    if tmp > dp[ss]:
        return dp[0]
    else:
        dp[ss] = tmp
    
    for a in reversed(range(ss)):
        tmp = 0
        for b in tree[a]:
            tmp += dp[b]
        dp[a] = tmp/len(tree[a]) + 1
    
    return dp[0]

for i in range(n-1):
    if len(tree[i]) == 1:
        continue
    for k in tree[i]:
        ans = min(ans,func(i,k))
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
ii = lambda : int(input())
mi = lambda : map(int,input().split())
li = lambda : list(map(int,input().split()))

n,m = mi()
tree = [[] for _ in range(n)]
for i in range(m):
    s,t = mi()
    tree[s-1].append(t-1)
dp = [0]*n
for i in reversed(range(n-1)):
    size = len(tree[i])
    for k in tree[i]:
        dp[i] += dp[k] 
    dp[i] /= size
    dp[i] += 1
ans = dp[0]

def func(ss,tt):
    dp_tmp = [0]*n
    for kk in range(ss+1,n):
        dp_tmp[kk] =dp[kk]
    tmp = 0
    for l in tree[ss]:
        if l == tt:
            continue
        tmp += dp_tmp[l]
    dp_tmp[ss] = tmp/(len(tree[ss])-1) + 1
    
    for a in reversed(range(ss)):
        tmp = 0
        for b in tree[a]:
            tmp += dp_tmp[b]
        dp_tmp[a] = tmp/len(tree[a]) + 1
    
    return dp_tmp[0]

for i in reversed(range(n-1)):
    if len(tree[i]) == 1:
        continue
    for k in tree[i]:
        ans = min(ans,func(i,k))
print(ans)






Fixed submission:
ii = lambda : int(input())
mi = lambda : map(int,input().split())
li = lambda : list(map(int,input().split()))

n,m = mi()
tree = [[] for _ in range(n)]
for i in range(m):
    s,t = mi()
    tree[s-1].append(t-1)
dp = [0]*n
for i in reversed(range(n-1)):
    size = len(tree[i])
    for k in tree[i]:
        dp[i] += dp[k] 
    dp[i] /= size
    dp[i] += 1
ans = dp[0]

def func(ss,tt):
    tmp = 0
    for l in tree[ss]:
        if l == tt:
            continue
        tmp += dp[l]
    tmp = tmp/(len(tree[ss])-1) + 1
    if tmp > dp[ss]:
        return dp[0]
    else:
        dp[ss] = tmp
    
    for a in reversed(range(ss)):
        tmp = 0
        for b in tree[a]:
            tmp += dp[b]
        dp[a] = tmp/len(tree[a]) + 1
    
    return dp[0]

for i in range(n-1):
    if len(tree[i]) == 1:
        continue
    for k in tree[i]:
        ans = min(ans,func(i,k))
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
ii = lambda : int(input())
mi = lambda : map(int,input().split())
li = lambda : list(map(int,input().split()))

n,m = mi()
tree = [[] for _ in range(n)]
for i in range(m):
    s,t = mi()
    tree[s-1].append(t-1)
import copy
dp = [0]*n
for i in reversed(range(n-1)):
    size = len(tree[i])
    for k in tree[i]:
        dp[i] += dp[k] 
    dp[i] /= size
    dp[i] += 1
ans = dp[0]
dp_tmp = copy.copy(dp)

def func(ss,tt):
    dp_tmp = copy.copy(dp)
    tmp = 0
    for l in tree[ss]:
        if l == tt:
            continue
        tmp += dp_tmp[l]
    dp_tmp[ss] = tmp/(len(tree[ss])-1) + 1
    
    for a in reversed(range(ss)):
        tmp = 0
        for b in tree[a]:
            tmp += dp_tmp[b]
        dp_tmp[a] = tmp/len(tree[a]) + 1
    
    return dp_tmp[0]

for i in reversed(range(n-1)):
    if len(tree[i]) == 1:
        continue
    for k in tree[i]:
        ans = min(ans,func(i,k))
print(ans)






Fixed submission:
ii = lambda : int(input())
mi = lambda : map(int,input().split())
li = lambda : list(map(int,input().split()))

n,m = mi()
tree = [[] for _ in range(n)]
for i in range(m):
    s,t = mi()
    tree[s-1].append(t-1)
dp = [0]*n
for i in reversed(range(n-1)):
    size = len(tree[i])
    for k in tree[i]:
        dp[i] += dp[k] 
    dp[i] /= size
    dp[i] += 1
ans = dp[0]

def func(ss,tt):
    tmp = 0
    for l in tree[ss]:
        if l == tt:
            continue
        tmp += dp[l]
    tmp = tmp/(len(tree[ss])-1) + 1
    if tmp > dp[ss]:
        return dp[0]
    else:
        dp[ss] = tmp
    
    for a in reversed(range(ss)):
        tmp = 0
        for b in tree[a]:
            tmp += dp[b]
        dp[a] = tmp/len(tree[a]) + 1
    
    return dp[0]

for i in range(n-1):
    if len(tree[i]) == 1:
        continue
    for k in tree[i]:
        ans = min(ans,func(i,k))
print(ans)