Uvalive 6398 Low Power

#include <iostream>
#include <cstdio>
#include <ctime>
#include <cstring>
#include <algorithm>
using namespace std;
const int MAXN=1000010;

int P[MAXN];
int N,K,num,ans;

bool fun(int mi){
for(int i=0,j=0,lab=1;i<N;i++,lab+=(2*K)){
for(;j<lab;j++){
if(P[j+1]-P[j]<=mi){
j+=2;
break;
}
}
if(j==lab){
return false;
}
}
return true;
}

int main(){
while(scanf("%d%d",&N,&K)!=EOF){
num=2*N*K;
for(int i=0;i<num;i++){
scanf("%d",&P[i]);
}
sort(P,P+num);
int l=0,r=P[num-1];
while(l<=r){
int mid=(l+r)>>1;
if(fun(mid)){
ans=mid;
r=mid-1;
}
else{
l=mid+1;
}
}
printf("%d\n",ans);
}
return 0;
}