849. Dijkstra求最短路 I

循环n次，每次用离源点最近的点去更新源点到其他点的距离。

#include<iostream>
#include<cstring>

using namespace std;

const int N = 510;
int dist[N];
int d[N][N];
int st[N];
int n, m;

int dijkstra(){
    dist[1] = 0;
    
    for(int i = 0; i < n; i ++){
        
        int k = 0;
        for(int j = 1; j <= n; j ++)
            if(st[j] == 0 && dist[j] < dist[k])
                k = j;
        
        st[k] = 1;
        for(int j = 1; j <= n; j ++)
            dist[j] = min(dist[j], dist[k] + d[k][j]);
    }
    
    if(dist[n] == 0x3f3f3f3f) return -1;
    return dist[n];
}

int main(){
    memset(dist, 0x3f, sizeof dist);
    memset(d, 0x3f, sizeof d);

    cin >> n >> m;
    
    for(int i = 1; i <= n; i ++) d[i][i] = 0;
    
    while(m --){
        int x, y, z;
        cin >> x >> y >> z;
        
        d[x][y] = min(d[x][y], z);
    }
    
    cout << dijkstra() << endl;
    
    return 0;
}