BFS遍历所有最短路线

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

typedef pair<int, int> Node;
#define x first
#define y second
const int N = 111111;
vector<int> nx[N];
int dist[N], n, m;
Node answer[N];

void BFS(const int x) {
    queue<int> q;

    memset(dist, 0x11, sizeof dist);
    dist[x] = 0;
    q.push(x);
    while (!q.empty()) {
        int u = q.front();

        q.pop();
        for (int i = 0; i < nx[u].size(); ++i) {
            int v = nx[u][i];

            if (dist[v] > dist[u] + 1) {
                dist[v] = dist[u] + 1;
                q.push(v);
            }
        }
    }
}

int BFS(int x, int y) {
    queue<int> q;

    for (int i = 0; i < N; ++i) {
        answer[i].x = INT_MAX;
        answer[i].y = 0;
    }
    answer[x].x = 0;
    answer[x].y = -dist[x];
    q.push(x);
    while (!q.empty()) {
        int u = q.front();

        q.pop();
        for (int i = 0; i < nx[u].size(); ++i) {
            int v = nx[u][i];

            if (answer[v] > Node(answer[u].x + 1, max(answer[u].y, -dist[v]))) {
                answer[v] = Node(answer[u].x + 1, max(answer[u].y, -dist[v]));
                q.push(v);
            }
        }
    }

    //cout << answer[y].x << ‘ ‘ << answer[y].y << endl;
    return -answer[y].y;
}

int Run() {
    int x, y, z;
    int a, b;

    while (cin >> n >> m) {
        for (int i = 1; i <= n; ++i) {
            nx[i].clear();
        }
        for (int i = 0; i < m; ++i) {
            cin >> a >> b;
            nx[a].push_back(b);
            nx[b].push_back(a);
        }
        cin >> x >> y >> z;
        BFS(z);
        cout << BFS(x, y) << endl;
    }

    return 0;
}

int main() {
    ios::sync_with_stdio(0);
    return Run();
}