poj 3268 Silver Cow Party (最短路算法的变换使用 【有向图的最短路应用】 )
2015-03-27 17:50
459 查看
Silver Cow Party
Description
One cow from each of N farms (1 ≤ N ≤ 1000) conveniently numbered 1..N is going to attend the big cow party to be held at farm #X (1 ≤ X ≤ N). A total of M (1 ≤ M ≤ 100,000) unidirectional (one-way roads connects pairs of farms; road i requires Ti (1 ≤ Ti ≤ 100) units of time to traverse.
Each cow must walk to the party and, when the party is over, return to her farm. Each cow is lazy and thus picks an optimal route with the shortest time. A cow's return route might be different from her original route to the party since roads are one-way.
Of all the cows, what is the longest amount of time a cow must spend walking to the party and back?
Input
Line 1: Three space-separated integers, respectively: N, M, and X
Lines 2..M+1: Line i+1 describes road i with three space-separated integers: Ai, Bi, and Ti. The described road runs from farm Ai to farm Bi, requiring Ti time units to traverse.
Output
Line 1: One integer: the maximum of time any one cow must walk.
Sample Input
Sample Output
Time Limit: 2000MS | Memory Limit: 65536K | |
Total Submissions: 13611 | Accepted: 6138 |
One cow from each of N farms (1 ≤ N ≤ 1000) conveniently numbered 1..N is going to attend the big cow party to be held at farm #X (1 ≤ X ≤ N). A total of M (1 ≤ M ≤ 100,000) unidirectional (one-way roads connects pairs of farms; road i requires Ti (1 ≤ Ti ≤ 100) units of time to traverse.
Each cow must walk to the party and, when the party is over, return to her farm. Each cow is lazy and thus picks an optimal route with the shortest time. A cow's return route might be different from her original route to the party since roads are one-way.
Of all the cows, what is the longest amount of time a cow must spend walking to the party and back?
Input
Line 1: Three space-separated integers, respectively: N, M, and X
Lines 2..M+1: Line i+1 describes road i with three space-separated integers: Ai, Bi, and Ti. The described road runs from farm Ai to farm Bi, requiring Ti time units to traverse.
Output
Line 1: One integer: the maximum of time any one cow must walk.
Sample Input
4 8 2 1 2 4 1 3 2 1 4 7 2 1 1 2 3 5 3 1 2 3 4 4 4 2 3
Sample Output
10 题目及算法分析: 代码:
#include <stdio.h> #include <string.h> #include <stdlib.h> #include <math.h> #include <ctype.h> #include <iostream> #include <string> #include <stack> #include <queue> #include <algorithm> #define N 1000+20 #define INF 0x3f3f3f3f using namespace std; int map ; int dis , ans ; bool vis ; int n, m, s; int Dijkstra(int s) { int i, j, k; for(i=1; i<=n; i++) dis[i]=map[s][i]; vis[s]=true; for(k=1; k<n; k++) { int mi=INF, pos; for(i=1; i<=n; i++) { if(vis[i]==false && dis[i]<mi ) { mi=dis[i]; pos=i; } } vis[pos]=true; for(j=1; j<=n; j++) { if(vis[j]==false && dis[j]>dis[pos]+map[pos][j] ) dis[j]=dis[pos]+map[pos][j]; } } for(i=1; i<=n; i++) { ans[i]=ans[i]+dis[i]; } return 0; } void turn_over() { for(int i=1; i<=n; i++) { for(int j=1; j<i; j++) swap(map[i][j], map[j][i] ); } } int main() { scanf("%d %d %d", &n, &m, &s); int u, v, w; for(int i=1; i<=n; i++) for(int j=1; j<=n; j++) { if(i==j) map[i][j]=0; else map[i][j]=INF; } for(int i=0; i<m; i++) { scanf("%d %d %d", &u, &v, &w); map[u][v] = w; } memset(vis, false, sizeof(vis)); memset(ans, 0, sizeof(ans)); Dijkstra(s); turn_over(); memset(vis, false, sizeof(vis)); Dijkstra(s); int cc=-1; for(int i=1; i<=n; i++) { if(ans[i]>cc && ans[i]<INF ) cc=ans[i]; } printf("%d\n", cc ); return 0; }
相关文章推荐
- poj 3268 Silver Cow Party (最短路算法的变换使用 【有向图的最短路应用】 )
- poj 3268 Silver Cow Party(最短路矩阵转置~)
- poj 3268 Silver Cow Party 【最短路Dijkstra + 结构体妙用】
- POJ 3268-Silver Cow Party【正向+反向最短路】
- poj 3268 Silver Cow Party 【最短路,有向图】
- POJ 3268 Silver Cow Party [双向最短路求最大值]
- POJ 3268 Silver Cow Party(最短路dijkstra)
- poj 3268 Silver Cow Party(最短路+SPFA)
- POJ 3268 - Silver Cow Party(最短路dijkstra)
- poj 3268 Silver Cow Party(最短路)
- POJ - 3268 Silver Cow Party (往返最短路,Floyd,Dijkstra 2次优化)
- poj 3268 Silver Cow Party(最短路)
- Poj 3268 Silver Cow Party + Poj 1511 Invitation Cards (最短路反向建图)
- POJ 3268——Silver Cow Party——————【最短路、Dijkstra、反向建图】
- POJ 3268 Silver Cow Party 最短路
- POJ - 3268 Silver Cow Party (逆向最短路 多源最短路)
- POJ 3268 Silver Cow Party(最短路 dijkstra求任意两点最短路)
- poj 3268 Silver Cow Party(最短路,正反两次,这个模版好)
- poj 3268 Silver Cow Party(最短路+SPFA)
- poj Silver Cow Party 3268 (来回单向最短路)好题