Problem p03256 (C++)

Buggy submission (status: Runtime Error):
/*
发现有解的充要条件是有一个形为AABBAABBAABB的环
此时每一个点至少与两个不同颜色的点相连
对于初始不合法的点直接删掉，判断删掉后与其相连的点是否变为不合法
类似拓扑排序
*/
#include <bits/stdc++.h>
#define gc getchar()
#define pc putchar
inline int read() {
  int x = 0, f = 1;
  char c = gc;
  while (c < '0' || c > '9') {
    if (c == '-')
      f = -1;
    c = gc;
  }
  while (c <= '9' && c >= '0')
    x = x * 10 + c - '0', c = gc;
  return x * f;
}
void print(long long x) {
  if (x < 0) {
    pc('-');
    x = -x;
  }
  if (x >= 10)
    print(x / 10);
  pc(x % 10 + '0');
}
const int maxn = 100007;
int val[maxn];
int n, m;
struct node {
  int v, next;
} edge[maxn];
int head[maxn], num = 0;
inline void add_edge(int u, int v) {
  edge[++num].v = v;
  edge[num].next = head[u];
  head[u] = num;
}
int d[maxn][2];
std::queue<int> q;
char s[maxn];
bool vis[maxn];
int main() {
  n = read(), m = read();
  scanf("%s", s + 1);
  for (int i = 1; i <= n; ++i) {
    char c = s[i];
    if (c == 'A')
      val[i] = 0;
    else
      val[i] = 1;
  }
  for (int u, v, i = 1; i <= m; ++i) {
    u = read(), v = read();
    add_edge(u, v);
    add_edge(v, u);
    d[u][val[v]]++, d[v][val[u]]++;
  }
  int count = 0;
  for (int i = 1; i <= n; ++i)
    if (!d[i][1] || !d[i][0])
      q.push(i), count++, vis[i] = 1;
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    for (int i = head[u]; i; i = edge[i].next) {
      int v = edge[i].v;
      d[v][val[u]]--;
      if ((!d[v][1] || !d[v][0]) && !vis[v]) {
        q.push(v);
        count++;
        vis[v] = 1;
      }
    }
  }
  puts(count == n ? "No" : "Yes");
  return 0;
}

Fixed submission:
/*
发现有解的充要条件是有一个形为AABBAABBAABB的环
此时每一个点至少与两个不同颜色的点相连
对于初始不合法的点直接删掉，判断删掉后与其相连的点是否变为不合法
类似拓扑排序
*/
#include <bits/stdc++.h>
#define gc getchar()
#define pc putchar
inline int read() {
  int x = 0, f = 1;
  char c = gc;
  while (c < '0' || c > '9') {
    if (c == '-')
      f = -1;
    c = gc;
  }
  while (c <= '9' && c >= '0')
    x = x * 10 + c - '0', c = gc;
  return x * f;
}
void print(long long x) {
  if (x < 0) {
    pc('-');
    x = -x;
  }
  if (x >= 10)
    print(x / 10);
  pc(x % 10 + '0');
}
const int maxn = 1000007;
int val[maxn];
int n, m;
struct node {
  int v, next;
} edge[maxn];
int head[maxn], num = 0;
inline void add_edge(int u, int v) {
  edge[++num].v = v;
  edge[num].next = head[u];
  head[u] = num;
}
int d[maxn][2];
std::queue<int> q;
char s[maxn];
bool vis[maxn];
int main() {
  n = read(), m = read();
  scanf("%s", s + 1);
  for (int i = 1; i <= n; ++i) {
    char c = s[i];
    if (c == 'A')
      val[i] = 0;
    else
      val[i] = 1;
  }
  for (int u, v, i = 1; i <= m; ++i) {
    u = read(), v = read();
    add_edge(u, v);
    add_edge(v, u);
    d[u][val[v]]++, d[v][val[u]]++;
  }
  int count = 0;
  for (int i = 1; i <= n; ++i)
    if (!d[i][1] || !d[i][0])
      q.push(i), count++, vis[i] = 1;
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    for (int i = head[u]; i; i = edge[i].next) {
      int v = edge[i].v;
      d[v][val[u]]--;
      if ((!d[v][1] || !d[v][0]) && !vis[v]) {
        q.push(v);
        count++;
        vis[v] = 1;
      }
    }
  }
  puts(count == n ? "No" : "Yes");
  return 0;
}