Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-

def is_reachable(adj, s, t):
    d = BFS(adj, s)
    if d[t] != -1:
        return True
    else:
        return False

def BFS(adj, start):
    n = len(adj)
    d = [-1] * n
    flag = [0] * n
    Q = []

    Q.append(start)
    d[start] = 0
    flag[start] = 1

    while len(Q) != 0:
        u = Q.pop(0)
        v = [i for i, x in enumerate(adj[u]) if (x == 1) and (flag[i] == 0)] # v := ??£??\???????????????????????¢?´¢??????????????????
        
        for i in v:
            Q.append(i)
            d[i] = d[u] + 1
            flag[i] = 1
    
    return d

def main():
    
    n, m = list(map(int, input().split()))
    adj = [[0 for i in range(n)] for j in range(n)]

    for i in range(m):
        s, t = list(map(int, input().split()))
        adj[s][t] = 1
        adj[t][s] = 1
    q = int(input())
    
    for i in range(q):
        s, t = list(map(int, input().split()))
        if is_reachable(adj, s, t):
            print("yes")
        else:
            print("no")
        
if __name__ == "__main__":
    main()    

Fixed submission:
# -*- coding: utf-8 -*-
import sys

def assignColor():
    for i in range(n):
        if C[i] == -1:
            DFS(i)

#@profile
def DFS(start):
    S = [start]
    C[start] = start
    while len(S) != 0:
        u = S.pop(0)
        for i in adj_list[u]:
            if C[i] == -1:
                C[i] = start
                S.append(i)

if __name__ == "__main__":
    _input = sys.stdin.readlines()
    n, m = list(map(int, _input[0].split()))
    adj_list = [[] for i in range(n)]
    C = [-1] * n
    
    for i in range(m):
        s, t = list(map(int, _input[i+1].split()))
        adj_list[s].append(t)
        adj_list[t].append(s)
    assignColor()
    q = int(_input[m+1])
    for i in range(q):
        s, t = list(map(int, _input[m+i+2].split()))
        if C[s] == C[t]:
            print("yes")
        else:
            print("no")

Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-

def assignColor(G):
    n = len(G)
    C = [-1 for i in range(n)]
    for i in range(n):
        if C[i] == -1:
            C = BFS(G, i, C)
    return C
        
def BFS(G, start, C):
    n = len(G)
    flag = [0] * n
    Q = []

    Q.append(start)
    C[start] = start
    flag[start] = 1

    while len(Q) != 0:
        u = Q.pop(0)
        v = [i for i in G[u] if flag[i] == 0] # v := ??£??\???????????????????????¢?´¢??????????????????
        
        for i in v:
            Q.append(i)
            C[i] = C[start]
            flag[i] = 1
    
    return C

def main():
    
    n, m = list(map(int, input().split()))
    G = [[] for i in range(n)]

    for i in range(m):
        s, t = list(map(int, input().split()))
        G[s].append(t)
        G[t].append(s)

    C = assignColor(G)
        
    q = int(input())
    
    for i in range(q):
        s, t = list(map(int, input().split()))
        if C[s] == C[t]:
            print("yes")
        else:
            print("no")
            
if __name__ == "__main__":
    main()    

Fixed submission:
# -*- coding: utf-8 -*-
import sys

def assignColor():
    for i in range(n):
        if C[i] == -1:
            DFS(i)

#@profile
def DFS(start):
    S = [start]
    C[start] = start
    while len(S) != 0:
        u = S.pop(0)
        for i in adj_list[u]:
            if C[i] == -1:
                C[i] = start
                S.append(i)

if __name__ == "__main__":
    _input = sys.stdin.readlines()
    n, m = list(map(int, _input[0].split()))
    adj_list = [[] for i in range(n)]
    C = [-1] * n
    
    for i in range(m):
        s, t = list(map(int, _input[i+1].split()))
        adj_list[s].append(t)
        adj_list[t].append(s)
    assignColor()
    q = int(_input[m+1])
    for i in range(q):
        s, t = list(map(int, _input[m+i+2].split()))
        if C[s] == C[t]:
            print("yes")
        else:
            print("no")

Buggy python submission (verdict: Runtime Error):
#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
static const int PLAYERS = 1025;
static const int ROUND = 11;

double ratings[PLAYERS];
double p[PLAYERS][ROUND];
int n;

double win(int p1, int p2) {
	return 1.0 / (1.0 + pow(10, (ratings[p2] - ratings[p1])/400.0));
}

double wp(int i, int k) {
  if (p[i][k] > 0) return p[i][k];
  if (k == 0) return p[i][k] = 1.0;
  /**
   * ?????????????????¢????????°??§????????????????§£?????¨????????????????????????
   */
  int index = i / (int)pow(2.0, k-1);
  int player;
  if (index % 2 == 0) {
    player = (index+1)*pow(2, k-1);
  } else {
    player = (index-1)*pow(2, k-1);
  }

  for (int j = 0; j < pow(2, k-1); j++){
    p[i][k] += wp(i,k-1)*win(i, player + j)*wp(player+j, k-1);
  }
  
  return p[i][k];
}

void solve_by_loop() {
	for (int i = 0; i < (int)pow(2.0, n); i++) {
		p[i][0] = 1.0;
	}
	for (int k = 1; k <= n; k++) {
		for (int i = 0; i < (int)pow(2.0, n); i++) {
			int index = i / (int)pow(2.0, k-1);
			int player;
			if (index % 2 == 0) {
				player = (index+1)*pow(2,k-1);
			} else {
				player = (index-1)*pow(2,k-1);
			}
			for (int j = 0; j < pow(2, k-1); j++) {
				p[i][k] += p[i][k-1]*win(i, player+j)*p[player+j][k-1];
			}
		}
	}
	for (int i = 0; i < pow(2, n); i++) {
		printf("%.10lf\n", p[i][n]);
	}
}
void solve() {
	for (int i = 0; i < (int)pow(2.0, n); i++) {
		printf("%.10lf\n", wp(i, n));
	}
}

int main() {
	cin >> n;
	for (int i = 0; i < (int)pow(2.0, n); i++) {
		cin >> ratings[i];
	}
	solve();
	//solve_by_loop();
	return 0;
}

Fixed submission:
# -*- coding: utf-8 -*-
import sys

def assignColor():
    for i in range(n):
        if C[i] == -1:
            DFS(i)

#@profile
def DFS(start):
    S = [start]
    C[start] = start
    while len(S) != 0:
        u = S.pop(0)
        for i in adj_list[u]:
            if C[i] == -1:
                C[i] = start
                S.append(i)

if __name__ == "__main__":
    _input = sys.stdin.readlines()
    n, m = list(map(int, _input[0].split()))
    adj_list = [[] for i in range(n)]
    C = [-1] * n
    
    for i in range(m):
        s, t = list(map(int, _input[i+1].split()))
        adj_list[s].append(t)
        adj_list[t].append(s)
    assignColor()
    q = int(_input[m+1])
    for i in range(q):
        s, t = list(map(int, _input[m+i+2].split()))
        if C[s] == C[t]:
            print("yes")
        else:
            print("no")

Buggy python submission (verdict: Runtime Error):
#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
static const int PLAYERS = 1025;
static const int ROUND = 11;

double ratings[PLAYERS];
double p[PLAYERS][ROUND];
int n;

double win(int p1, int p2) {
	return 1.0 / (1.0 + pow(10, (ratings[p2] - ratings[p1])/400.0));
}

double wp(int i, int k) {
  if (p[i][k] > 0) return p[i][k];
  if (k == 0) return p[i][k] = 1.0;
  /**
   * ?????????????????¢????????°??§????????????????§£?????¨????????????????????????
   */
  int index = i / (int)pow(2.0, k-1);
  int player;
  if (index % 2 == 0) {
    player = (index+1)*pow(2, k-1);
  } else {
    player = (index-1)*pow(2, k-1);
  }

  for (int j = 0; j < pow(2, k-1); j++){
    p[i][k] += wp(i,k-1)*win(i, player + j)*wp(player+j, k-1);
  }
  
  return p[i][k];
}

void solve_by_loop() {
	for (int i = 0; i < (int)pow(2.0, n); i++) {
		p[i][0] = 1.0;
	}
	for (int k = 1; k <= n; k++) {
		for (int i = 0; i < (int)pow(2.0, n); i++) {
			int index = i / (int)pow(2.0, k-1);
			int player;
			if (index % 2 == 0) {
				player = (index+1)*pow(2,k-1);
			} else {
				player = (index-1)*pow(2,k-1);
			}
			for (int j = 0; j < pow(2, k-1); j++) {
				p[i][k] += p[i][k-1]*win(i, player+j)*p[player+j][k-1];
			}
		}
	}
	for (int i = 0; i < pow(2, n); i++) {
		printf("%.10lf\n", p[i][n]);
	}
}
void solve() {
	for (int i = 0; i < (int)pow(2.0, n); i++) {
		printf("%.10lf\n", wp(i, n));
	}
}

int main() {
	cin >> n;
	for (int i = 0; i < (int)pow(2.0, n); i++) {
		cin >> ratings[i];
	}
	solve();
	//solve_by_loop();
	return 0;
}

Fixed submission:
# -*- coding: utf-8 -*-
import sys

def assignColor():
    for i in range(n):
        if C[i] == -1:
            DFS(i)

#@profile
def DFS(start):
    S = [start]
    C[start] = start
    while len(S) != 0:
        u = S.pop(0)
        for i in adj_list[u]:
            if C[i] == -1:
                C[i] = start
                S.append(i)

if __name__ == "__main__":
    _input = sys.stdin.readlines()
    n, m = list(map(int, _input[0].split()))
    adj_list = [[] for i in range(n)]
    C = [-1] * n
    
    for i in range(m):
        s, t = list(map(int, _input[i+1].split()))
        adj_list[s].append(t)
        adj_list[t].append(s)
    assignColor()
    q = int(_input[m+1])
    for i in range(q):
        s, t = list(map(int, _input[m+i+2].split()))
        if C[s] == C[t]:
            print("yes")
        else:
            print("no")