python/TangDou/AcWing/EulerPath/LianTongXing/floyd.cpp

#include <bits/stdc++.h>

using namespace std;

const int N = 1010; // 图的最大点数量
int n, m;

// 用floyd来判断起点是否可以达到终点
int g[N][N]; // 邻接矩阵
void floyd() {
    for (int k = 1; k <= n; k++)
        for (int i = 1; i <= n; i++)
            for (int j = 1; j <= n; j++)
                g[i][j] = g[i][j] || (g[i][k] && g[k][j]);
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("in1.in", "r", stdin);
    // freopen("in2.in", "r", stdin);
#endif

    // 采用邻接矩阵建图
    cin >> n >> m;
    // m条边
    for (int i = 1; i <= m; i++) {
        int a, b;
        cin >> a >> b;
        // 双向建边
        g[a][b] = 1, g[b][a] = 1;
    }
    // 调用floyd
    floyd();

    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            if (!g[i][j]) {
                printf("图不是连通的\n");
                cout << i << " " << j << endl;
                exit(0);
            }
    printf("图是连通的\n");
    return 0;
}