POJ 2456 Aggressive cows （二分搜索）

Aggressive cows

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 7495		Accepted: 3743

Description

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

最大化最小值  不能的话说明太大了 可以的说明太小 挑战经典check函数

AC代码如下：

//
//  Created by TaoSama on 2015-04-18
//  Copyright (c) 2015 TaoSama. All rights reserved.
//
#include <algorithm>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <string>
#include <set>
#include <vector>

using namespace std;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
const int N = 1e5 + 10;

int n, c, a[N];

bool check(int x) {
	int last = 1;
	for(int i = 2; i <= c; ++i){
		int idx = last + 1;
		while(idx <= n && a[idx] - a[last] < x)
			idx++;
		if(idx == n + 1) return false;
		last = idx;
	}
	return true;
}

int main() {
#ifdef LOCAL
    freopen("in.txt", "r", stdin);
//  freopen("out.txt","w",stdout);
#endif
    ios_base::sync_with_stdio(0);

    scanf("%d%d", &n, &c);
    for(int i = 1; i <= n; ++i) scanf("%d", a + i);
    sort(a + 1, a + 1 + n);
    int l = 0, r = 1e9 + 1;
    while(l + 1 < r) {
        int mid = 0LL + l + r >> 1;
        if(check(mid)) l = mid;
        else r = mid;
    }
    printf("%d\n", l);
    return 0;
}