POJ2456——二分——Aggressive cows

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?

Input

* Line 1: Two space-separated integers: N and C 

* Lines 2..N+1: Line i+1 contains an integer stall location, xi

Output

* Line 1: One integer: the largest minimum distance

Sample Input

5 3
1
2
8
4
9

Sample Output

3

Hint

OUTPUT DETAILS: 

FJ can put his 3 cows in the stalls at positions 1, 4 and 8, resulting in a minimum distance of 3. 

Huge input data,scanf is recommended.

/*
二分经典题
大意  n头牛让你放m头要求这些牛之间的最小距离在所有情况里面的最大值
判断的时候移动下标
*/
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int inf = 0x3f3f3f3f;
const int MAX = 1e6 + 10;
int n, m;
int a[MAX];

bool check(int x)
{
    int last = 1;
    int cur;
    for(int i = 1; i <= m - 1; i++){
        cur = last + 1;
        while(cur <= n && a[cur] - a[last] <= x)
        cur++;
        last = cur;
        if(cur == n + 1) return false;
    }
       return true;
}

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