51nod 1105 第K大的数

#include <bits/stdc++.h>using namespace std;long long a[50050],b[50050];long long n,k;long long bersum(long long x){long long i,tmp,ret=0;for(i=0;i<n;i++){tmp=x/a[i]+1;ret+=n-(lower_bound(b,b+n,tmp)-b);}return ret;}int main(){long long i,lef,rig,mid;while(cin>>n>>k){for(i=0;i<n;i++)scanf("%lld%lld",&a[i],&b[i]);sort(a,a+n);sort(b,b+n);lef=a[0]*b[0];rig=a[n-1]*b[n-1];while(lef<=rig){mid=(lef+rig)>>1;if(bersum(mid)>=k)lef=mid+1;elserig=mid-1;} printf("%lld\n",lef);}}