求助！！WA一个点P7

#include <bits/stdc++.h>
using namespace std;
const long long maxn = 999999999;
int R,C;
int graph[102][102];
int least[102][102];
bool b[102][102];
int minn = 0;
int dir[5][2] = {
    {0,0},{-1,0},{0,-1},{0,1},{1,0}
};
bool check(int x,int y){
    for(register int i(1);i <= 4;i++){
        if(x + dir[i][0] > R || y + dir[i][1] > C
        || x + dir[i][0] < 1 || y + dir[i][1] < 1){continue;}
        else if(!b[x + dir[i][0]][y + dir[i][1]] 
        && graph[x + dir[i][0]][y + dir[i][1]] < graph[x][y]){return 0;}
    }
    return 1;
}
int dfs(int x,int y,int sum){
    if(check(x,y)){
        minn = max(minn,sum);
        least[x][y] = 1;
        return 1;
    }
    int pre = 0;
    for(register int i(1);i <= 4;i++){
        if(!b[x + dir[i][0]][y + dir[i][1]] 
            && graph[x + dir[i][0]][y + dir[i][1]] < graph[x][y]
            && x + dir[i][0] <= R && y + dir[i][1] <= C
            && x + dir[i][0] >= 1 && y + dir[i][1] >= 1){
            if(least[x + dir[i][0]][y + dir[i][1]] != 0){
                    if(sum + least[x + dir[i][0]][y + dir[i][1]] <= minn){continue;}
            }
            b[x + dir[i][0]][y + dir[i][1]] = 1;
            pre = dfs(x + dir[i][0],y + dir[i][1],sum + 1)+1;
            least[x][y] = max(least[x][y],pre);
            b[x + dir[i][0]][y + dir[i][1]] = 0;
        }
    }
    return pre;
}
int main()
{
    cin >> R >> C;
    for(register int i(1);i<=R;i++)
    for(register int j(1);j<=C;j++){
        cin >> graph[i][j];
    }
    for(register int i(1);i<=R;i++)
    for(register int j(1);j<=C;j++){
        b[i][j] = 1;
        dfs(i,j,0);
        b[i][j] = 0;
    }
    cout << minn+1;
    return 0;
}