C++ :

#include<bits/stdc++.h>
using namespace std;  
//四个可以走的方向 
int fx[5]={0,1,-1,0,0};  
int fy[5]={0,0,0,1,-1};  

//泳池的深度 
int swim[101][101];  

//标记是否走过 
bool f[101][101];  
int n,m,ans;  

//从x、y位置开始 
int find(int x,int y)  
{  
    //如果该路线没走过 
    if(f[x][y] == false){ 
	    int tot=1;  
	    //标记为走过 
	    f[x][y]=true;  
	    //遍历四个方向 
	    for(int i=1;i<=4;++i)  
	    {  
	        //将要走到的位置 
	        int dx=x+fx[i];  
	        int dy=y+fy[i];  
	        //如果将要走到的位置和本位置相同，且不越界 
	        if(swim[x][y]==swim[dx][dy]&&dx>0&&dy>0&&dx<=n&&dy<=m&&!f[dx][dy])  
	                tot+=find(dx,dy);  
	    }  
	    return tot;  
    } else{
    	return 0;
	} 
    
}  
int main()  
{  
    cin>>n>>m;
    string c;
	//计算二维数组的值  
    for(int i=1;i<=n;++i)  
    {  
        cin>>c;  
        for(int j=0;j<m;++j) swim[i][j+1]=c[j]-'0';
    }  
    //循环从每个点开始回溯找最大面积 
    for(int i=1;i<=n;++i)  
        for(int j=1;j<=n;++j)  
            ans=max(ans,find(i,j));  
    cout<<ans<<endl;
    return 0;  
}

Java :

import java.util.Scanner;
import java.util.Stack;
public class Main {
	public static void main(String[]args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		if(n>=1&&n<=100&&m>=1&&m<=100){
			int[][]map = new int[n+2][m+2];				  
			int[][]move = {{0,1},{0,-1},{1,0},{-1,0}};
			for(int i=0 ;i<n+2 ;i++){
				map[i][0] = 0;
				map[i][m+1] = 0;
			}
			for(int i=0 ;i<m+2 ;i++){
				map[0][i] = 0;
				map[n+1][i] = 0;
			}
			String[]s = new String[n];
			for(int i=0 ;i<n ;i++){
				s[i] = sc.next();
			}
			for(int i=1 ;i<=n ;i++){
				for(int j=1 ;j<=m ;j++){
					map[i][j] = s[i-1].charAt(j-1)-48;
				}
			}
			Stack s1 = new Stack();	
			int result = Dfs(map,s1,move,n,m);
			System.out.println(result);
		}
		
	}
	public static int Dfs(int[][]maze,Stack s,int[][]move,int n,int m){	
		int Max = Integer.MIN_VALUE;
		int[][]visited = new int[n+1][m+1];
		for(int i=1 ;i<=n;i++){
			for(int j=1 ;j<=m;j++){								
					int times = 0;
					visited[i][j]=-1;
					Step temp = new Step(i,j,-1);			
					s.push(temp);								
					while(!s.isEmpty()){
						temp = (Step) s.peek();
						int x = temp.x;
						int y = temp.y;
						int d = temp.d+1;
						while(d<4){
							int xx = x+move[d][0];
							int yy = y+move[d][1];
							if(maze[x][y] == maze[xx][yy]&&visited[xx][yy]==0){
								temp = new Step(xx,yy,-1);			
								s.push(temp);
								x=xx;
								y=yy;
								visited[x][y]=-1;
								d=0;			
								
							}else{
								d++;
							}
						}
						if(d==4){						
							s.pop();
							times++;				
						}
					}
					if(times>Max){
						Max = times;
					}
			}
				}
		return Max;
	}
}
class Step{												
	int x,y,d;
	Step(int x,int y,int d){
		this.x = x;
		this.y = y;
		this.d = d;
	}
}