poj 2456 Aggressive cows （二分）

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<iostream>
using namespace std;
int n,c;
int a[100000+100];

int solve(int m)
{
    int ret=1;
    int i,j,k;
    int l=0,r;
    for(i=1;i<n;i++)
    {
        if(a[i]-a[l]>=m)
        {
            ret++;
            l=i;
        }
    }
    return ret;
}

/*
bool solve(int x)  
{  
    int cnt = 1, tmp = a[0];  
    for(int i = 1; i < n; i++)  
    {  
        if(a[i] - tmp >= x)  
        {  
            cnt++;  
            tmp = a[i];  
            if(cnt >= c) //可以放下C头牛  
                return true;  
        }  
    }  
    return false;  
} */


int erfen(int l,int r)
{
    //printf("%d......\n",solve(2));
    while(l<=r)
    {
        int m=(l+r)>>1;
        //printf("%d %d %d\n",l,m,r);
        //printf("sol %d %d\n",m,solve(m));
        if(solve(m)>=c)
        //if(solve(m))
        {
            l=m+1;
        }
        else //if(solve(m)<c)
        {
            r=m-1;
        }
        //printf("%d %d..\n",l,r);
    }
    //if(solve(r)==c) return r;
    return l;
}

int main()
{
    int i,j,k;
    while(scanf("%d%d",&n,&c)!=EOF)
    {
        for(i=0;i<n;i++)
        {
            scanf("%d",&a[i]);
        }
        sort(a,a+n);
       
        
        int ans;
        ans=erfen(0,a[n-1]-a[0]);
        printf("%d\n",ans-1);
    }
    return 0;
}