代码如下

#include<iostream>
#include<vector>
using namespace std;
int main(){
int x1,y1,x2,y2;
cin>>x1>>y1>>x2>>y2;
vector<vector<long long>>dp(x1+20,vector<long long>(y1+20,0));
for(int i=0;i<=x1;i++)dp[i][0]=1;
for(int j=0;j<=y1;j++)dp[0][j]=1;
if(x2!=x1&&y2!=y1){
dp[x2][y2]=-1;
}
if(x2-1>=0&&y2-2>=0&&x2!=x1&&y2!=y1){
dp[x2-1][y2-2]=-1;
}
if(y2-2>=0&&x2!=x1&&y2!=y1){
dp[x2+1][y2-2]=-1;
}
if(x2-2>=0&&y2-1>=0&&x2!=x1&&y2!=y1){
dp[x2-2][y2-1]=-1;
}
if(x2-2>=0&&x2!=x1&&y2!=y1){
dp[x2-2][y2+1]=-1;
}
if(x2-1>=0&&x2!=x1&&y2!=y1){
dp[x2-1][y2+2]=-1;
}
if(x2!=x1&&y2!=y1){
dp[x2+1][y2+2]=-1;
}
if(y2-1>=0&&x2!=x1&&y2!=y1){
dp[x2+2][y2-1]=-1;
}
if(x2!=x1&&y2!=y1){
dp[x2+2][y2+1]=-1;
}
for(int i=1;i<=x1;i++){
for(int j=1;j<=y1;j++){
if(dp[i][j]!=-1){
if(dp[i-1][j]!=-1)dp[i][j]+=dp[i-1][j];
if(dp[i][j-1]!=-1)dp[i][j]+=dp[i][j-1];
}
}
}
cout<<dp[x1][y1];
}