79. 单词搜索

class Solution {
        private int rows;
        private int cols;
        private int wordLength;
        private boolean[][] hasUse;
        private char[] charArray;
        private char[][] board;

        public boolean exist(char[][] board, String word) {
            rows = board.length;
            if (rows == 0) {
                return false;
            }
            cols = board[0].length;

            wordLength = word.length();
            charArray = word.toCharArray();
            hasUse = new boolean[rows][cols];
            this.board = board;

            for (int i = 0; i < rows; i++) {
                for (int j = 0; j < cols; j++) {
                    if (dfs(i, j, 0)) {
                        return true;
                    }
                }
            }
            return false;
        }


        private boolean dfs(int i, int j, int currCharIndex) {
            //判断是否已使用，是否点在区域内
            if (!isArea(i, j)||hasUse[i][j]){
                return false;
            }

            //结束条件
            if (currCharIndex == wordLength - 1) {
                return board[i][j] == charArray[currCharIndex];
            }

            if (board[i][j] == charArray[currCharIndex]) {
                //上下左右的尝试
                hasUse[i][j] = true;
                boolean res = dfs(i + 1, j, currCharIndex + 1) || dfs(i - 1, j, currCharIndex + 1)
                        || dfs(i, j + 1, currCharIndex + 1) || dfs(i, j - 1, currCharIndex + 1);

                if (res) {
                    return true;
                }
                hasUse[i][j] = false;
            }

            return false;

        }

        private boolean isArea(int i, int j) {
            return i >= 0 && i < rows && j >= 0 && j < cols;
        }
    }