Floyd : 最小环

https://www.acwing.com/problem/content/346/

#include <bits/stdc++.h>
using namespace std;
#define IO ios::sync_with_stdio(false);cin.tie(0); cout.tie(0)
inline int lowbit(int x) { return x & (-x); }
#define ll long long
#define pb push_back
#define PII pair<int, int>
#define x first
#define y second
#define inf 0x3f3f3f3f
const int N = 110;
int n, m;
int d[N][N], g[N][N];
int pos[N][N];
int path[N], cnt;

void get_path(int i, int j) {
    if (pos[i][j] == 0) return;
    int k = pos[i][j];
    get_path(i, k);
    path[cnt++] = k;
    get_path(k, j);
}

int main() {
    IO;
    cin >> n >> m;
    memset(g, 0x3f, sizeof g);
    for (int i = 1; i <= n; ++i) g[i][i] = 0;
    while (m--) {
        int a, b, c;
        cin >> a >> b >> c;
        g[a][b] = g[b][a] = min(g[a][b], c);
    }
    int res = inf;
    memcpy(d, g, sizeof d);
    for (int k = 1; k <= n; ++k) {
        for (int i = 1; i < k; ++i)
            for (int j = i + 1; j < k; ++j)
                if ((ll)d[i][j] + g[j][k] + g[k][i] < res) {
                    res = d[i][j] + g[j][k] + g[k][i];
                    cnt = 0;
                    path[cnt++] = k;
                    path[cnt++] = i;
                    get_path(i, j);
                    path[cnt++] = j;
                }
    }
        for (int i = 1; i <= n; ++i)
            for (int j = 1; j <= n; ++j) 
                if (d[i][j] > d[i][k] + d[k][j]) {
                    d[i][j] = d[i][k] + d[k][j];
                    pos[i][j] = k;
                }
    if (res == inf) puts("No solution.");
    else {
        for (int i = 0; i < cnt; ++i) cout << path[i] << ' ';
        cout << endl;
    }
    return 0;
}