POJ 2456 Aggressive cows

#include <cstdio>
#include <algorithm>
using namespace std;

const int MAXN = 100000+5;
int a[MAXN];
int n, c;

bool ok(int d)
{
    int pre = 0;
    for(int i = 1; i < c; ++i){
        int cur = pre+1;
        while(cur < n && a[cur]-a[pre] < d)
            ++cur;
        if(cur == n)
            return false;
        pre = cur;
    }
    return true;
}

int main()
{
    scanf("%d%d", &n, &c);
    for(int i = 0; i < n; ++i)
        scanf("%d", &a[i]);
    sort(a, a+n);
    int l = 0, r = 0x7fffffff;
    while(r-l > 1){
        int mid = (l+r)/2;
        if(ok(mid)) l = mid;
        else r = mid;
    }
    printf("%d\n", l);
    return 0;
}