求Graph里两点间最短距离，可以容纳负值边；可以检测出negative circle

int bellmanFord(int n[][N], int start, int dest) {
	int dist[N];
	int path[N];
	int i, j, k;
	for(i = 0; i < N; i++) {
		dist[i] = -1;
	}


	dist[dest] = 0;
	for(i = 0; i < N - 1; i++) {
		for(j = 0; j < N; j++) {
			//graph is adjacent matrix, take O(n) time to find the min edge?
			int minEdge = 0x0FFFFFFF;
			for(k = 0; k < N; k++) {
				if(graph[j][k] != -1) {
					minEdge = (minEdge > graph[j][k]) ? graph[j][k] : minEdge;
				}
			}

			dist[j] = (dist[j] > dist[j - 1] + minEdge) ? (dist[j - 1] + minEdge) : dist[j];
		}
	}

	return dist[start];
}

改进以后可以记载shortest path的路径，使用数组path[N]

int bellmanFord(int n[][N], int start, int dest) {
	int dist[N];
	int path[N];
	int i, j, k;
	for(i = 0; i < N; i++) {
		dist[i] = -1;
	}

	dist[dest] = 0;
	for(i = 0; i < N - 1; i++) {
		for(j = 0; j < N; j++) {
			//graph is adjacent matrix, take O(n) time to find the min edge?
			int minEdge = 0x0FFFFFFF;
			int edgeTail;
			for(k = 0; k < N; k++) {
				if(graph[j][k] != -1) {
					if(minEdge > graph[j][k]) {
						minEdge = graph[j][k];
						edgeTail = k;
					}
				}
			}

			if(dist[j] > dist[j - 1] + minEdge) {
				path[j] = edgeTail;
				dist[j] = dist[j - 1] + minEdge;
			}
		}
	}

	//output the path 
	int pathPosition = start;
	while(pathPosition != dest) {
		cout<<pathPosition<<" -> ";
		pathPosition = path[pathPosition];
	}
	cout<<dest<<endl;

	
	return dist[start];
}