过河卒 DP

#include<bits/stdc++.h>
using namespace std;

using LL = long long;
int n,m,x,y;
int horse[30][30];
LL dp[30][30];

void init()
{
    int dx[]={2,1,-1,-2,-2,-1,1,2,0};
    int dy[]={1,2,2,1,-1,-2,-2,-1,0};
    for(int i=0;i<9;i++)
    {   
        int a = x+dx[i];
        int b = y+dy[i];
        if(a<=n && a>=0 && b<=m && b>=0)
        {
            horse[a][b]=1;
        }
    }
}


int main()
{   
    cin>>n>>m>>x>>y;
    init();

    dp[0][0]=1;
    for(int i=0;i<=n;i++)
    {
        for(int j=0;j<=m;j++)
        {   
            if(i==0&&j==0) continue;
            if(horse[i][j]) dp[i][j]=0; 
            else if(i==0) dp[i][j] = dp[i][j-1];
            else if(j==0) dp[i][j] = dp[i-1][j];
            else dp[i][j] = dp[i-1][j]+dp[i][j-1];
        }
    }

    cout<<dp[n][m];
    return 0;
}