POJ 1154

#include<iostream>
#include<stdio.h>
#define MAXN 20
using namespace std;

int DFS(int i,int j,int len,int r,int c);
bool key[26];
char a[MAXN][MAXN];
//bool bool_lean[MAXN][MAXN];
int main()
{
    //freopen("acm.acm","r",stdin);
    int i;
    int j;
    int r;
    int c;
    cin>>r>>c;
//    memset(bool_lean,false,sizeof(bool_lean));
    for(i = 0; i < r; ++ i)
    {
        for(j = 0; j < c; ++ j)
        {
            cin>>a[i][j];
        }
    }
    key[a[0][0]-‘A‘] = true;
    cout<<DFS(0,0,1,r,c)<<endl;
}

int DFS(int i,int j,int len,int r,int c)
{
    int tem;
    tem = len;
    int max = 0;
    if(i > 0)
    {
        if(!key[a[i-1][j] - ‘A‘])
        {
            key[a[i-1][j] - ‘A‘] = true;
        //    bool_lean[i-1][j] = true;
            len = DFS(i-1,j,len+1,r,c);
            key[a[i-1][j] - ‘A‘] = false;
        //    bool_lean[i-1][j] = false;
            if(len > max)
                max = len;
            len = tem;
        }
    
    }
    if(i < r-1)
    {
        if(!key[a[i+1][j] - ‘A‘])
        {
            key[a[i+1][j] - ‘A‘] = true;
        //    bool_lean[i+1][j] = true;
            len = DFS(i+1,j,len+1,r,c);
            key[a[i+1][j] - ‘A‘] = false;
        //    bool_lean[i+1][j] = false;
            if(len > max)
                max = len;
            len = tem;
        }

    }
    if(j > 0)
    {
        if(!key[a[i][j-1] - ‘A‘])
        {
            key[a[i][j-1] - ‘A‘] = true;
        //    bool_lean[i][j-1] = true;
            len = DFS(i,j-1,len+1,r,c);
            key[a[i][j-1] - ‘A‘] = false;
        //    bool_lean[i][j-1] = false;
            if(len>max)
                max = len;
            len = tem;
        }
    }
    if(j < c-1)
    {
        if(!key[a[i][j+1] - ‘A‘])
        {
            key[a[i][j+1] - ‘A‘] = true;
    //        bool_lean[i][j+1] = true;
            len = DFS(i,j+1,len+1,r,c);
            key[a[i][j+1] - ‘A‘] = false;
    //        bool_lean[i][j+1] = false;
            if(len>max)
                max = len;
            len = tem;
        }
    }    
    if(len > max)
        max = len;
    return max;
}