剑指Offer——JZ65.矩阵中的路径【DFS】

题目传送门

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题解

• 使用 DFS + 回溯

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AC-Code

class Solution {
	int dx[4] = { 0, 0, 1, -1 };
	int dy[4] = { 1, -1, 0, 0 };
	bool** vis;
public:
	bool hasPath(char* matrix, int rows, int cols, char* str) {
		vis = new bool* [rows];
		for (int i = 0; i < rows; ++i) {
			vis[i] = new bool[cols];
			memset(vis[i], false, sizeof(bool) * cols);
		}
		bool flag = false;
		int x, y;
		for (int i = 0; i < strlen(matrix) && !flag; ++i) {
			if (matrix[i] == str[0]) {
				x = i / cols;
				y = i % cols;
				vis[x][y] = true;
				flag = dfs(x, y, matrix, rows, cols, str, 0);
				vis[x][y] = false;
			}
		}
		delete[] vis;
		return flag;
	}
	bool dfs(int x, int y, char* matrix, int rows, int cols, char* str, int index) {
		if (index + 1 == strlen(str))
			return true;
		for (int i = 0; i < 4; ++i) {
			int nx = x + dx[i];
			int ny = y + dy[i];
			if (judge(nx, ny, matrix, rows, cols, str, index + 1)) {
				vis[nx][ny] = true;
				if (dfs(nx, ny, matrix, rows, cols, str, index + 1))	// 这里最开始手误写成++index了。不能++，因为回溯的时候，index必须保持之前的值
					return true;
				vis[nx][ny] = false;
			}
		}
		return false;
	}
	bool judge(int x, int y, char* matrix, int rows, int cols, char* str, int index) {
		if (x < 0 || x >= rows || y < 0 || y >= cols)    return false;
		return matrix[x * cols + y] == str[index] && !vis[x][y];
	}
};