第K小数

类似于K’th
二分+two point

#include <cstdio>#include <iostream>#include <algorithm>using namespace std;long long l=0,r,k;long long a[2100000],b[2100000];int n,m;bool check(long long mid){    long long t1=1,t2=m,sum1=0;    while(t1<=n&&t2>=1)    {        while(a[t1]*b[t2]>mid&&t2>=1) t2--;        sum1+=t2;        t1++;    }    return sum1<k;}void get_ans(){    sort(a+1,a+n+1);    sort(b+1,b+m+1);     r=a[n]*b[m]+2;    while(l<=r)     {        long long mid=(l+r)/2;        if(check(mid)) l=mid+1;        else           r=mid-1;     }    printf("%lld",l);}int main(){    freopen("number.in","r",stdin);    freopen("number.out","w",stdout);    scanf("%d%d%lld",&n,&m,&k);    for(int i=1;i<=n;i++)     scanf("%d",&a[i]);    for(int i=1;i<=m;i++)     scanf("%d",&b[i]);     get_ans();    return 0;}