POJ 1734 Sightseeing Trip (最小環)

#include <stdio.h>
#define MAX_POINTS 101
#define INF 300000

int numOfPoints, numOfRoads;
int initialDist[MAX_POINTS][MAX_POINTS];
int shortestDist[MAX_POINTS][MAX_POINTS];
int pre[MAX_POINTS][MAX_POINTS];
int path[MAX_POINTS];
int num;

int getMin(int x, int y){
	return x < y ? x : y;
}

int main(){
	//freopen("input.txt", "r", stdin);

	while (scanf("%d", &numOfPoints) != EOF){
		if (numOfPoints == -1)
			break;
		int from, to;
		for (from = 1; from <= numOfPoints; from++)
			for (to = 1; to <= numOfPoints; to++){
				initialDist[from][to] = shortestDist[from][to] = INF;
				pre[from][to] = from;
			}

		scanf("%d", &numOfRoads);
		int dist;
		int i;
		for (i = 1; i <= numOfRoads; i++){
			scanf("%d%d%d", &from, &to, &dist);
			initialDist[from][to] = shortestDist[from][to] = initialDist[to][from] = shortestDist[to][from] = getMin(dist, initialDist[from][to]);
		}

		int minLen = INF;
		int pass;
		for (pass = 1; pass <= numOfPoints; pass++){
			//遍歷所有環，from-> (因爲最小環要求不經過相同的景點，所以走不包含pass的最短路，因爲還沒計算呢) -> to -> pass -> from
			for (from = 1; from < pass; from++)
				for (to = from + 1; to < pass; to++){
					int routeLen = shortestDist[from][to] + initialDist[from][pass] + initialDist[pass][to];
					if (routeLen < minLen){
						minLen = routeLen;
						int prePoint = to;
						num = 0;
						while (prePoint != from){
							path[num++] = prePoint;
							prePoint = pre[from][prePoint];
						}
						path[num++] = from;
						path[num++] = pass;
					}
				}

			for (from = 1; from <= numOfPoints; from++)
				//需記錄路徑，不能對稱優化
				for (to = 1; to <= numOfPoints; to++)
					if (shortestDist[from][pass] + shortestDist[pass][to] < shortestDist[from][to]){
						shortestDist[from][to] = shortestDist[from][pass] + shortestDist[pass][to];
						pre[from][to] = pre[pass][to];
					}
		}

		if (minLen == INF)
			printf("No solution.\n");
		else {
			for (i = 0; i < num; i++)
				printf("%d ", path[i]);
			printf("\n");
		}

	}

	return 0;
}