USACO 2005 Nov Cow Acrobats 奶牛杂技

#include<cstdio>
#include<cstdlib>
#include<ctime>
int n,s[50001],w[50001],sw[50001];
void swap(int *a,int *b)
{
int temp;
temp=*a;
*a=*b;
*b=temp;
}
void sort(int l,int r)
{
int key=sw[rand()%(r-l+1)+l];
int i=l,j=r;
while(i<=j)
{
while(sw[i]<key)
i++;
while(sw[j]>key)
j--;
if(i<=j)
{
swap(&s[i],&s[j]);
swap(&w[i],&w[j]);
swap(&sw[i],&sw[j]);
i++;
j--;
}
}
if(l<j)
sort(l,j);
if(i<r)
sort(i,r);
}
int main()
{
srand(time(NULL));
freopen("acrobat.in","r",stdin);
freopen("acrobat.out","w",stdout);
scanf("%d",&n);
for(int i=1;i<=n;i++)
{
scanf("%d%d",&w[i],&s[i]);
sw[i]=w[i]+s[i];
}
sort(1,n);
long long int max=-s[1];
long long int add=0;
for(int i=1;i<=n;i++)
{
if(max<=add-s[i])
{
max=add-s[i];
}
add+=w[i];
}
printf("%lld\n",max);
return 0;
}