Submission #384888

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Source Code Expand

#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <fstream>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
using namespace std;
typedef long long ll;
#define REP(i, N) for (int i = 0; i < (int)N; i++)
const int INF = 1 << 30;
const ll MOD = 1e9 + 7;
typedef pair<int, int> P;

int N, a, b, M;

vector<int> edges[101];

int ds[101];
int c[101];

int main() {
  cin >> N >> a >> b >>M;
  REP(i,M) {
    int x, y;
    cin >> x >> y;
    edges[x].push_back(y);
    edges[y].push_back(x);
  }

  queue<int> queue;
  REP(i,N+1) ds[i] = -1;

  queue.push(a);
  ds[a] = 0;
  c[a] = 1;

  while(queue.size()) {
    int n = queue.front(); queue.pop();
    for(int nn: edges[n]) {
      if(ds[nn] == -1) {
        queue.push(nn);
        ds[nn] = ds[n] + 1;
        c[nn] = c[n];
      } else if (ds[nn] == ds[n] + 1) {
        c[nn] += c[n];
        c[nn] %= MOD;
      }
    }
  }
  cout << c[b] << endl;
  return 0;
}

Submission Info

Judge Result