func_code_string: #include <bits/stdc++.h>   using namespace std;   const int MOD = 1e9 + 7;   const int MAXN = 1e3 + 5;   const int INF = 0x3f3f3f3f;   const double eps = 1e-9;   short int mp[MAXN][MAXN];   int d[MAXN][2];   bool vis[MAXN];   int n, m, s, t, u, v;   void dijkstra(int s, int idx) {     memset(vis, false, sizeof(vis));     for (int i = 1; i <= n; i++) d[i][idx] = INF;     d[s][idx] = 0;     for (int i = 0; i < n; i++) {       int x = -1, m = INF;       for (int j = 1; j <= n; j++)         if (!vis[j] && d[j][idx] < m) m = d[x = j][idx];       if (x != -1) {         vis[x] = true;         for (int j = 1; j <= n; j++) {           if (mp[x][j] == 1 && d[j][idx] > d[x][idx] + 1) {             d[j][idx] = d[x][idx] + 1;           }         }       }     }   }   int main() {     scanf( %d %d %d %d , &n, &m, &s, &t);     for (int i = 0; i < m; i++) {       scanf( %d %d , &u, &v);       mp[u][v] = mp[v][u] = 1;     }     dijkstra(s, 0);     dijkstra(t, 1);     int ans = 0;     for (int i = 1; i <= n; i++) {       for (int j = i + 1; j <= n; j++) {         if (mp[i][j] == 0 && d[i][0] + d[j][1] + 1 >= d[t][0] &&             d[i][1] + d[j][0] + 1 >= d[t][0])           ans++;       }     }     printf( %d n , ans);     return 0;   }   