【剑指Offer】12. 矩阵中的路径

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 r = 0, idx = 0; r < rows; r++)
        for (int c = 0; c < cols; c++)
            matrix[r][c] = array[idx++];
    return matrix;
}