POJ--2456--Aggressive cows

题目描述：
Farmer John has built a new long barn, with N (2 <= N <= 100,000) stalls. The stalls are located along a straight line at positions x1,…,xN (0 <= xi <= 1,000,000,000).

His C (2 <= C <= N) cows don’t like this barn layout and become aggressive towards each other once put into a stall. To prevent the cows from hurting each other, FJ want to assign the cows to the stalls, such that the minimum distance between any two of them is as large as possible. What is the largest minimum distance?
输入描述:
Line 1: Two space-separated integers: N and C
Lines 2…N+1: Line i+1 contains an integer stall location, xi
输出描述:
Line 1: One integer: the largest minimum distance
输入：
5 3
1
2
8
4
9
输出：
3
题意：
有n个牛栏，选m个放进牛，相当于一条线段上有 n 个点，选取 m 个点，
使得相邻点之间的最小距离值最大
题解：
最大值最小化，最小化最大值的问题全部都是二分
代码：

#include
#include
#include
#include
using namespace std;

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

bool bsearch(int x){
    int cnt = 1;
    int last = a[0];
    for(int i = 1; i < n; i ++){
        if(a[i] - last >= x){
            cnt ++;
            last = a[i];
        }
    }
    if(cnt >= c) return true;
    return false;
}

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