$Floyd$ 算法

依次枚举中心点更新最短距离

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
const int INF = 1e9;


int n,m;
vector<vector<int>> adj,pre;

//回溯路径
vector<int> get_path(int s,int e){
	vector<int> path;
	if (adj[s][e]==INF) return {};
	
	int cur = e;
	while (1){
		path.push_back(cur);
		
		if (cur==s) break;
		cur = pre[s][cur];
	}
	
	reverse(path.begin(),path.end());
	return path;
}

void solve(){
	cin >> n >> m;
	adj = vector<vector<int>>(n,vector<int>(n,INF));
	pre = vector<vector<int>>(n,vector<int>(n,-1));
	
	for (int i=0;i<m;i++){
		int u,v,w;
		cin >> u >> v >> w;
		u--,v--;
		adj[u][v] = adj[v][u] = w;
		
		pre[u][v] = u;
		pre[v][u] = v;
	}
	for (int i=0;i<n;i++){
		adj[i][i] = 0;
		pre[i][i] = i;
	}
	
	for (int k=0;k<n;k++){
		for (int i=0;i<n;i++){
			if (adj[i][k]==INF) continue;
			for (int j=0;j<n;j++){
				if (adj[k][j]==INF) continue;
				if (adj[i][k]+adj[k][j] < adj[i][j]){
					adj[i][j] = adj[i][k]+adj[k][j];
					pre[i][j] = pre[k][j];
				}
			}
		}
	}
	
	for (int i=0;i<n;i++){
		for (int j=0;j<n;j++){
			cout << adj[i][j];
			if (j==n-1) cout << '\n';
			else cout << ' ';
		}
	}
}


int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	
	solve();
	
	return 0;
}