hdu4370 dijkstra矩阵转单向边最短路矩阵+自环闭环

Posted 2021-01-13 zsben991126

/*

矩阵太神奇了Orz，网上的题解大多是spfa，不过我发想dijkstra也能做

把n*n的矩阵看成是单向边距离矩阵就行

*/

#include<iostream>
#include<cstring>
#include<cstdio>
#include<queue>
#define MAXN 500
#define INF 1<<30
using namespace std;
int a[MAXN][MAXN];
int n;
int dist[MAXN],vis[MAXN];
int dijkstra(int s,int t){
    memset(dist,0,sizeof dist); 
    memset(vis,0,sizeof vis);
    for(int i=0;i<=n;i++)
        if(i==s)
            dist[i]=INF;
        else 
            dist[i]=a[s][i];
    
    while(1){
        int k=-1;
        int Min=INF;
        for(int i=1;i<=n;i++)
            if(!vis[i]&&dist[i]<Min){
                Min=dist[i];
                k=i;
            }
        if(k==-1)
            break;
        vis[k]=true;
        for(int i=1;i<=n;i++)
            if(!vis[i]&&dist[i]>dist[k]+a[k][i])
                dist[i]=dist[k]+a[k][i];
    }
    return dist[t];
}
int main(){
    while(scanf("%d",&n)==1){
        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++)
                scanf("%d",&a[i][j]);
        
        printf("%d
",min(dijkstra(1,n),dijkstra(1,1)+dijkstra(n,n)));
    }
    return 0;
}