BZOJ 4525 二分

//By SiriusRen
#include <cstdio>
#include <algorithm>
using namespace std;
int n,k,a[500050],ans;
bool check(int x){
    int rec=0;
    for(int i=1;i<=n;){
        int temp=a[i]+2*x;rec++;
        while(a[i]<=temp&&i<=n)i++;
    }return rec<=k;
}
int main(){
    scanf("%d%d",&n,&k);
    for(int i=1;i<=n;i++)scanf("%d",&a[i]);
    sort(a+1,a+1+n);
    int l=0,r=0x3f3f3f3f;
    while(l<=r){
        int mid=(l+r)>>1;
        if(check(mid))ans=mid,r=mid-1;
        else l=mid+1;
    }printf("%d\n",ans);
}