題目鏈接：http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=GRL_1_C

All Pairs Shortest Path

Input
An edge-weighted graph G (V, E).

|V| |E|
s0 t0 d0
s1 t1 d1
:
s|E|?1 t|E|?1 d|E|?1
|V| is the number of vertices and |E| is the number of edges in G. The graph vertices are named with the numbers 0, 1,…, |V|?1 respectively.

si and ti represent source and target vertices of i-th edge (directed) and di represents the cost of the i-th edge.

Output
If the graph contains a negative cycle (a cycle whose sum of edge costs is a negative value), print

NEGATIVE CYCLE
in a line.

Otherwise, print

D0,0 D0,1 … D0,|V|?1
D1,0 D1,1 … D1,|V|?1
:
D|V|?1,0 D1,1 … D|V|?1,|V|?1
The output consists of |V| lines. For each ith line, print the cost of the shortest path from vertex i to each vertex j (j=0,1,…|V|?1) respectively. If there is no path from vertex i to vertex j, print “INF”. Print a space between the costs.

Constraints
1 ≤ |V| ≤ 100
0 ≤ |E| ≤ 9900
-2 × 107 ≤ di ≤ 2 × 107
There are no parallel edges
There are no self-loops
Sample Input 1
4 6
0 1 1
0 2 5
1 2 2
1 3 4
2 3 1
3 2 7
Sample Output 1
0 1 3 4
INF 0 2 3
INF INF 0 1
INF INF 7 0

Sample Input 2
4 6
0 1 1
0 2 -5
1 2 2
1 3 4
2 3 1
3 2 7
Sample Output 2
0 1 -5 -4
INF 0 2 3
INF INF 0 1
INF INF 7 0

Sample Input 3
4 6
0 1 1
0 2 5
1 2 2
1 3 4
2 3 1
3 2 -7
Sample Output 3
NEGATIVE CYCLE

這題先用Bellman-Ford算法判斷負圈，再用Floyd-Warshall算法求任意兩點間的最短路即可。

代碼：

#include <iostream> #include <algorithm> #include <map> #include <vector> using namespace std; typedef long long ll; #define INF 2147483647struct edge{int from,to,cost; };edge es[10000];int d[110][110]; // d[i][j]表示點i到點j的最短路徑 int V,E; //點和邊的數量 //判斷負圈 bool find_negative_loop(){int s[110];fill(s,s+V,0);for(int i = 0;i < V; i++){for(int j = 0;j < E; j++){edge e = es[j];if(s[e.to] > s[e.from] + e.cost){s[e.to] = s[e.from] + e.cost;if(i == V-1) return false;}}}return true; }//任意兩點間最短路徑 void warshall_floyd(){for(int k = 0;k < V; k++){for(int i = 0;i < V; i++){for(int j = 0;j < V; j++){if(d[i][k] != INF && d[k][j] != INF)d[i][j] = min(d[i][j], d[i][k] + d[k][j]);}}} }int main(){cin >> V >> E;for(int i = 0;i < V; i++){for(int j = 0;j < V; j++){d[i][j] = INF;}d[i][i] = 0;}for(int i = 0;i < E; i++) cin >> es[i].from >> es[i].to >> es[i].cost,d[es[i].from][es[i].to] = es[i].cost;if(find_negative_loop()){warshall_floyd();for(int i = 0;i < V; i++){for(int j = 0;j < V; j++){if(j != 0) cout << " ";if(d[i][j] == INF) cout << "INF";else cout << d[i][j];}cout << endl;}}else{cout <<"NEGATIVE CYCLE" <<endl;}return 0; }

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