Submission #1774835

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Source Code Expand

#include<bits/stdc++.h>
using namespace std;
const int M = 1000000007;

int main() {
    int n, m, s, t;
    cin >> n >> m >> s >> t;
    --s;
    --t;
    vector<vector<int>> edge(n);
    for (int i = 0; i < m; ++i) {
        int a, b;
        scanf("%d%d", &a, &b);
        --a;
        --b;
        edge[a].push_back(b);
        edge[b].push_back(a);
    }
    vector<int> ds(n, -1);
    vector<int> cs(n, 0);
    queue<int> q;
    q.push(s);
    ds[s] = 0;
    ++cs[0];
    while (!q.empty()) {
        int p = q.front();
        q.pop();
        for (int i : edge[p]) {
            if (ds[i] == -1) {
                ds[i] = ds[p] + 1;
                ++cs[ds[i]];
                q.push(i);
            }
        }
    }
    vector<int> dt(n, -1);
    vector<int> ct(n, 0);
    q.push(t);
    dt[t] = 0;
    ++ct[0];
    while (!q.empty()) {
        int p = q.front();
        q.pop();
        for (int i : edge[p]) {
            if (dt[i] == -1) {
                dt[i] = dt[p] + 1;
                ++ct[dt[i]];
                q.push(i);
            }
        }
    }
    int l = ds[t] - 1;
    long long ans = 0;
    for (int i = 0; i <= l; ++i)
        ans += cs[i] * (long long)ct[l - i - 1];

    cout << ans << "\n";
    return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:13:30: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d", &a, &b);
                              ^

Judge Result