HDU 1596 find the safest road

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http://acm.hdu.edu.cn/showproblem.php?pid=1596

1.队列优化的SPFA算法

#include <queue>#include <stdio.h>#include <string.h>#include <iostream>#include <algorithm>using namespace std;const int Max = 1010;typedef pair <double,int> pii;int n,m,vis[Max];double safe[Max],map[Max][Max];void SPFA(int scr){///SPFA重复入队，用队列减少无用的松弛    for(int i=1; i<=n; i++)        safe[i] = 0, vis[i] = 0;    safe[scr] = 1,vis[scr] = 1;    queue <int> q;    q.push(scr);    while(!q.empty()){        int tmp = q.front();q.pop();        vis[tmp]=0;        for(int i=1; i<=n; i++){            if(safe[i] < safe[tmp] * map[tmp][i]){                safe[i] = safe[tmp] * map[tmp][i];                if(!vis[i]){                    q.push(i);                    vis[i] = 1;                }            }        }    }}int main(){//    freopen("in.txt", "r", stdin);    while(scanf("%d",&n) == 1 && n){        for(int i=1; i<=n; i++){            for(int j=1; j<=n; j++){                scanf("%lf",&map[i][j]);            }        }        scanf("%d",&m);        int from, to;        for(int i=0; i<m; i++){            scanf("%d%d",&from, &to);            SPFA(from);            if(!safe[to])   puts("What a pity!");            else printf("%.3lf\n",safe[to]);        }    }    return 0;}

2.优先队列优化的dijkstra

#include <queue>#include <stdio.h>#include <string.h>#include <iostream>#include <algorithm>using namespace std;const int Max = 1010;typedef pair <double,int> pii;int n,m,vis[Max];double safe[Max],map[Max][Max];void dijkstra(int scr){///每一次贪心选择最优    for(int i=1; i<=n; i++)        safe[i] = 0, vis[i] = 0;    safe[scr] = 1;    priority_queue <pii> q;    q.push(make_pair(safe[scr], scr));    while(!q.empty()){        pii tmp = q.top();q.pop();        int from = tmp.second;//        cout << from << endl;        if(vis[from]) continue;        vis[from]=1;        for(int i=1; i<=n; i++){            if(safe[i] < safe[from] * map[from][i]){                safe[i] = safe[from] * map[from][i];                q.push(make_pair(safe[i], i));            }        }    }}int main(){//    freopen("in.txt", "r", stdin);    while(scanf("%d",&n) == 1 && n){        for(int i=1; i<=n; i++){            for(int j=1; j<=n; j++){                scanf("%lf",&map[i][j]);            }        }        scanf("%d",&m);        int from, to;        for(int i=0; i<m; i++){            scanf("%d%d",&from, &to);            dijkstra(from);            if(!safe[to])   puts("What a pity!");            else printf("%.3lf\n",safe[to]);        }    }    return 0;}

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