穷举vs暴搜vs深搜vs回溯vs剪枝系列一＞单词搜索

class Solution {
    private boolean[][] visit;//标记使用过的数据
    int m,n;//行，列
    char[] word;

    public boolean exist(char[][] board, String _word) {
        m = board.length;
        n = board[0].length;
        visit = new boolean[m][n];
        word = _word.toCharArray();

        for(int i = 0; i < m; i++)
            for(int j = 0; j < n; j++){
                if(word[0] == board[i][j]){
                    visit[i][j] = true;
                    if(dfs(board,i,j,1)) return true;
                    visit[i][j] = false;//恢复现场
                }
            }
        return false;    
    }

    int[] dx = {0,0,-1,1};
    int[] dy = {-1,1,0,0};


    boolean dfs(char[][]board, int i, int j, int pos){
        if(pos == word.length){
            return true;//搜索成功
        }

        for(int k = 0; k < 4; k++) {
            int x = i + dx[k]; 
            int y = j + dy[k];

            if(x >= 0 && x < m && y >= 0 && y < n && !visit[x][y] && word[pos] == board[x][y]){
                visit[x][y] = true;
                if(dfs(board,x,y,pos+1)) return true;
                visit[x][y] = false;//恢复现场
            }
        }

        return false;
    }
}