自己證明(交換法):
#include<cstdio>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<string>
#define ll long long
using namespace std;
struct aa
{
ll a,b;
}s[1000009];
int n;
ll ans=-0x3f3f3f3f;
bool cmp(aa a,aa b)
{
return a.a+a.b<b.a+b.b;
}
int main()
{
scanf("%d",&n);
for (int i=1;i<=n;i++) scanf("%lld%lld",&s[i].a,&s[i].b);
sort(s+1,s+n+1,cmp);//排序
int r=0;
for (int i=1;i<=n;i++)
{
if (r-s[i].b>ans) ans=r-s[i].b;
r+=s[i].a;
}//程式看似沒有多麼高深,這個貪心關鍵全在前面的證明裡的,交換法證貪心!!!!!!!!!!!
printf("%lld",ans);
return 0;
}