python/TangDou/CSP-J/J2_2019/4_1.cpp

#include <bits/stdc++.h>
using namespace std;

typedef pair<int, int> PII;
#define x first
#define y second

const int N = 1e5 + 10, M = N << 1;

// 20个测试点，过了7个，得了35分,其它TLE
// 邻接表
int e[M], h[N], idx, ne[M];
void add(int a, int b) {
    e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}
bool bfs(int start, int dist) {
    queue<PII> q;
    q.push({start, dist});

    while (q.size()) {
        auto u = q.front();
        q.pop();

        if (u.x == 1 && u.y == 0) return true; // 在用完所有步数后，到达1号点，成功！

        for (int i = h[u.x]; ~i; i = ne[i]) {
            int v = e[i];
            if (u.y) q.push({v, u.y - 1});
        }
    }
    return false;
}

int main() {
    // 链式前向星
    memset(h, -1, sizeof h);

    int n, m, Q;
    cin >> n >> m >> Q;

    while (m--) {
        int a, b;
        cin >> a >> b;
        add(a, b), add(b, a); // 无向图，双向建边
    }

    while (Q--) {
        int u, dist;
        cin >> u >> dist;
        cout << (bfs(u, dist) ? "Yes" : "No") << endl;
    }
    return 0;
}