Solution12.java

package com.usher.algorithm.offer;

/**
 * @Author: Usher
 * @Description:
 * 矩阵中的路径
 * 用一个状态数组保存之前访问过的字符，然后再分别按上下左右递归
 * ?
 */
public class Solution12 {
    private final static int[][] next = {{0, -1}, {0, 1}, {-1, 0}, {1, 0}};
    private int rows;
    private int cols;

    public boolean hasPath(char[] array, int rows, int cols, char[] str) {
        if (rows == 0 || cols == 0)
            return false;
        this.rows = rows;
        this.cols = cols;
        boolean[][] marked = new boolean[rows][cols];
        char[][] matrix = buildMatrix(array);
        for (int i = 0; i < rows; i++)
            for (int j = 0; j < cols; j++)
                if (backtracking(matrix, str, marked, 0, i, j))
                    return true;
        return false;
    }

    private boolean backtracking(char[][] matrix, char[] str, boolean[][] marked, int pathLen, int r, int c) {
        if (pathLen == str.length)
            return true;
        if (r < 0 || r >= rows || c < 0 || c >= cols || matrix[r][c] != str[pathLen] || marked[r][c])
            return false;
        marked[r][c] = true;
        for (int[] n : next)
            if (backtracking(matrix, str, marked, pathLen + 1, r + n[0], c + n[1]))
                return true;
        marked[r][c] = false;
        return false;
    }

    private char[][] buildMatrix(char[] array) {
        char[][] matrix = new char[rows][cols];
        for (int i = 0, idx = 0; i < rows; i++)
            for (int j = 0; j < cols; j++)
                matrix[i][j] = array[idx++];
        return matrix;
    }
}