思路：
1. dfs
2. 记录一下parent， 不能走parent
3. 如果遇到visit 过的肯定有cycle
4. 无向图找cycle


代码：


class Solution {
    boolean visit[][];
    int sr=-1;int sc=-1;
    boolean yes=false;
    Set<String>set=new HashSet<>();
    public boolean containsCycle(char[][] grid) {
        visit=new boolean[grid.length][grid[0].length];
        for(int i=0;i<grid.length;i++){
            for(int j=0;j<grid[0].length;j++){
                if(visit[i][j])continue;
                dfs(grid,i,j,grid[i][j],-1,-1);
                if(yes)return true;
            }
        }
        
        return false;
    }
    
    public void dfs(char[][] grid,int r,int c,char cc,int lastr,int lastc){
        if(r<0||c<0||r>=grid.length||c>=grid[0].length)return;

        if(grid[r][c]!=cc)return;
       
        
        if(visit[r][c]&&grid[r][c]==cc){
            yes=true;
            return;
        }
        
        
        visit[r][c]=true;
        if(r+1!=lastr||c!=lastc){
            dfs(grid,r+1,c,cc,r,c);
        }
        
        if(r-1!=lastr||c!=lastc){
            dfs(grid,r-1,c,cc,r,c);
        }
        
        if(r!=lastr||c+1!=lastc){
            dfs(grid,r,c+1,cc,r,c);
        }
        
        if(r!=lastr||c-1!=lastc){
            dfs(grid,r,c-1,cc,r,c);
        }
    }
    
}