USACO 2.4 Bessie Come Home (Floyd最短路径)

最新推荐文章于 2020-02-08 18:05:22 发布

原创最新推荐文章于 2020-02-08 18:05:22 发布 · 351 阅读

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#USACO #2.4 #Bessie Come Home #Floyd #最短路径

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本文展示了一个使用C语言实现的图算法示例，通过定义牧场间的距离矩阵并利用Floyd-Warshall算法来找出任意两点间最短路径。代码中详细介绍了如何读取输入文件、解析牧场间的连接及距离，并更新距离矩阵以反映最短路径。

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#include <stdio.h>
#define DEBUG 1
#define TESTCASES 9
#define INF 1e8

int distanceMatrix[52][52];

int char2Int(char cha){
	if (cha >= 'A' && cha <= 'Z')
		return cha - 'A';
	else
		return cha - 'a' + 26;;
}

int main(){
#if DEBUG
	int testCase;
	for (testCase = 1; testCase <= TESTCASES; testCase++){
		char inputFileName[20] = "input7.txt";
		//inputFileName[5] = '1' +  (testCase - 1);
		freopen(inputFileName, "r", stdin);
		printf("\n#%d\n", testCase);
#endif

	int from, to;
	for (from = 0; from < 52; from++)
		for (to = from; to < 52; to++)
			if (from == to)
				distanceMatrix[from][to] = 0;
			else
				distanceMatrix[from][to] = distanceMatrix[to][from] = INF;

	int numOfPaths;
	scanf("%d", &numOfPaths);
	char cha;
	int path;
	for (path = 1; path <= numOfPaths; path++){
		char onePasture, anotherPasture;
		int distance;
		scanf("%c", &cha);
		scanf("%c %c %d", &onePasture, &anotherPasture, &distance);
		from = char2Int(onePasture);
		to = char2Int(anotherPasture);
		if (distance < distanceMatrix[from][to])
			//相同的两个牧场之间可能有多条路，选最短的
			distanceMatrix[from][to] = distanceMatrix[to][from] = distance;	
	}

	int pass;
	for (pass = 0; pass < 52; pass++)
		for (from = 0; from < 52; from++)
			for (to = from + 1; to < 52; to++)
				if (distanceMatrix[from][pass] + distanceMatrix[pass][to] < distanceMatrix[from][to])
					distanceMatrix[from][to] = distanceMatrix[to][from] = distanceMatrix[from][pass] + distanceMatrix[pass][to];

	char result;
	int minDistance = INF;
	to = 25;
	for (from = 0; from < 25; from++)
		if (distanceMatrix[to][from] < minDistance){
			result = from;
			minDistance = distanceMatrix[to][from];
		}

	printf("%c %d\n", 'A' + result, minDistance);

#if DEBUG
	}
#endif
	return 0;
}