C :

#include <stdlib.h>
#include <stdio.h>

int x[100005],N,C;
int cmp(const void *a, const void *b)
{
    return(*(int *)a-*(int *)b);
}
int f(int a)
{
    int i,s=1,p=0;
    for(i=1; p+i<N; i++)
    {
        if(x[p+i]-x[p]>=a)
        {
            p=p+i;
            s++;
            i=0;
        }
    }
    if(s>=C) return 1;
    else return 0;
}
int main()
{
    int i,a,b,c,ans;
    while(~scanf("%d%d",&N,&C))
    {
        for(i=0; i<N; i++) scanf("%d",&x[i]);
        qsort(x,N,sizeof(x[0]),cmp);
        a=1;
        b=x[N-1]-x[0];
        while(a<=b)
        {
            c=(a+b)/2;
            if(f(c))
            {
                a=c+1;
                ans=c;
            }
            else b=c-1;
        }
        printf("%d\n",ans);
    }
    return 0;
}

C++ :

#include<stdio.h>
#include<algorithm>
using namespace std;
int a[100010],n,c;
bool greed( int t)
{
    int i,j=a[0],count=0;
    for(i=0;i<n;i++)
    {
        if(a[i]-j>=t) {j=a[i];  count++;}
        if(count>=c-1) return true;

    }
    return false;
}
void binary_search()
{
    int front=0,end=a[n-1]-a[0];
    int mid;

    while(front<=end)
    {
        mid=(front + end )/2;
        if(greed(mid))
            front=mid+1;
           else end=mid-1;
    }
    printf("%d\n",front-1);
}
int main()
{
    int i;
    while(scanf("%d %d",&n,&c)!=EOF)
    {
        for(i=0;i<n;i++)
          scanf("%d",&a[i]);
          sort(a,a+n);
          binary_search();
    }
    return 0;
}