矩阵中的路径

深度优先

class Solution {
    public boolean exist(char[][] board, String word) {
       char[] words = word.toCharArray();
       int m = words.length;
       boolean[][] visit = new boolean[board.length][board[0].length];
       for(int i=0;i<board.length;i++){
           for(int j=0;j<board[0].length;j++){
               if(board[i][j] == words[0]){//找到起始位置
                   if(dfs(i,j,visit,0,board,words)) return true;
               }
           }
       }
       return false;
    }
    private boolean dfs(int i,int j,boolean[][]visit, int index,char[][]board,char[] words){
        if(index == words.length) return true;
        if(i < 0 || i >= board.length || j < 0 || j >= board[0].length
        || board[i][j] != words[index] || visit[i][j]){
            return false;
        }
        visit[i][j] = true;
        boolean flag = dfs(i+1,j,visit,index+1,board,words)//四个方向尝试
                     ||dfs(i,j+1,visit,index+1,board,words)
                     ||dfs(i-1,j,visit,index+1,board,words)
                     ||dfs(i,j-1,visit,index+1,board,words);
        visit[i][j] = false;
        return  flag;   

    }
}