Floyd AcWing 854. Floyd求最短路

梦里梦外; 2023-09-28 12:48 113阅读 0赞

## Floyd AcWing 854. Floyd求最短路 ##

### 原题链接 ###

[AcWing 854. Floyd求最短路][AcWing 854. Floyd]

### 算法标签 ###

最短路 Floyd

### 思路 ###

![在这里插入图片描述][86b66de68e96477695369b80563be2c9.png]

### 代码 ###

#include<bits/stdc++.h>
    #define int long long
    #define rep(i, a, b) for(int i=a;i<b;++i)
    #define Rep(i, a, b) for(int i=a;i>b;--i)
    using namespace std;
    const int N = 205, INF = 0x3f3f3f3f;
    int d[N][N];
    int n,m,k;
    inline int read(){
       int s=0,w=1;
       char ch=getchar();
       while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();}
       while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
       return s*w;
    }
    void put(int x) {
        if(x<0) putchar('-'),x=-x;
        if(x>=10) put(x/10);
        putchar(x%10^48);
    }
    void fl(){
        rep(k, 1, n+1){
            rep(i, 1, n+1){
                rep(j, 1, n+1){
                    d[i][j]=min(d[i][j], d[i][k]+d[k][j]);
                }
            }
        }
    }
    signed main(){
        ios::sync_with_stdio(false);
        cin.tie(0);
        cout.tie(0);
        n=read(), m=read(), k=read();
        rep(i, 1, n+1){
            rep(j, 1, n+1){
                if(i-j){
                    d[i][j]=INF;
                }else{
                    d[i][j]=0;
                }
            }
        }
        while(m--){
            int x=read(), y=read(), z=read();
            d[x][y]=min(d[x][y], z);
        }
        fl();
        while(k--){
            int x=read(), y=read();
            if(d[x][y]>INF/2){
                puts("impossible");
            }else{
                printf("%lld\n", d[x][y]);
            }
        }
        return 0;
    }

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![在这里插入图片描述][9cb4cb80a18345158f8a69e2f196e5b9.png]

[AcWing 854. Floyd]: https://www.acwing.com/problem/content/856/
[86b66de68e96477695369b80563be2c9.png]: https://img-blog.csdnimg.cn/86b66de68e96477695369b80563be2c9.png
[9cb4cb80a18345158f8a69e2f196e5b9.png]: https://img-blog.csdnimg.cn/9cb4cb80a18345158f8a69e2f196e5b9.png