贪心 No Time for Dragons Gym - 101149B

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 200005
using namespace std;
typedef struct
{
    int x,y;
}Point;
Point a[maxn];
int cmp(Point b,Point c)
{
    return b.y> c.y;
}
int main()
{
    long long ans=0;
    int n;
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        int x1,y1;
        cin>>x1>>y1;
        a[i].x=x1,a[i].y=x1-y1;
    }
    sort(a+1,a+n+1,cmp);
    ans+=a[1].x;
    for(int i=2;i<=n;i++)
    {
        if(a[i].x>a[i-1].y)
         ans+=(a[i].x-a[i-1].y);
         else
             a[i].y+=(a[i-1].y-a[i].x);

    }
 cout<<ans<<endl;
}