USACO 2.4 Overfencing (BFS)

最新推荐文章于 2021-12-15 19:28:34 发布

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#USACO #2.4 #Overfencing BFS

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本文介绍了一种使用C++实现的迷宫最短路径寻找算法。通过定义迷宫结构并采用广度优先搜索（BFS）策略，从迷宫的出口逆向寻找到达起点的最短路径。该算法利用了结构体节点来记录位置和步数，并通过队列进行节点的存储和处理。

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<pre name="code" class="cpp">#include <stdio.h>
#define DEBUG 1
#define TESTCASES 9

int map[300][100];
typedef struct Node{
	int row;
	int column;
	int steps;
}Node;
Node queue[20000];
int head, tail;
Node NodePushed, NodePoped;
int directionArray[4][2] = {-1, 0, 1, 0, 0, -1, 0, 1};

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

	int height, width;
	char cha;
	scanf("%d%d", &width, &height);
	//注意字符的输入处理,过滤掉换行符
	scanf("%c", &cha);
	int heightLines = (height << 1) + 1;
	int widthLines = (width << 1) + 1;

	head = tail = 0;	
	int row, column;
	for (row = 0; row < heightLines; row++){
		for (column = 0; column < widthLines; column++){
			scanf("%c", &cha);
			if (cha == '+' || cha == '-' || cha == '|')
				map[row][column] = 0;
			else if (row == 0 || row == heightLines - 1 || column == 0 || column == widthLines - 1){
				//从出口处开始逆向BFS会使得问题变得简单很多
				NodePushed.row = row;
				NodePushed.column = column;
				//出口处的步数初始化为1，没有藩篱的位置都当作可以行走，最终的步数除以2便可以
				NodePushed.steps = 1;
				queue[tail++] = NodePushed;
			} else
				map[row][column] = 1;
		}
		scanf("%c", &cha);
	}

	while (head < tail){
		NodePoped = queue[head++];
		int directionIndex;
		for (directionIndex = 0; directionIndex < 4; directionIndex++){
			row = NodePoped.row + directionArray[directionIndex][0];
			column = NodePoped.column + directionArray[directionIndex][1];
			if (row >= 0 && row < heightLines && column >= 0 && column < widthLines && map[row][column] == 1){
				map[row][column] = 0;
				NodePushed.row = row;
				NodePushed.column = column;
				NodePushed.steps = NodePoped.steps + 1;
				queue[tail++] = NodePushed;
			}
		}
	}

	printf("%d\n", queue[tail - 1].steps >> 1);

#if DEBUG
	}
#endif
	return 0;
}