WA最后一个点 求求

#include<bits/stdc++.h>
using namespace std;
int n,a[1005],b[1005],f[1005][10005],p = 5001,ans = 0;
int main(){
	memset(f,0x3f3f3f,sizeof(f));
	cin >> n; 
	for(int i = 1;i <= n; i++)
		cin >> a[i] >> b[i]; 
	f[1][a[1]-b[1]+p] = 0;
	f[1][b[1]-a[1]+p] = 1;
	for(int i = 2;i <= n; i++){
		for(int j = -5000;j <= 5000; j++)
			f[i][j+p] = min(f[i-1][j-(a[i]-b[i])+p],f[i-1][j-(b[i]-a[i])+p]+1);
	}
	for(int i = 0;i <= 5000;i ++){
		if(f[n][i+p] <= 1000||f[n][-i+p] <= 1000){
			ans = min(f[n][i+p],f[n][-i+p]);
			break;
		}
	}
	cout << ans;
    return 0;
}