poj 2456

Aggressive cows
Time Limit: 1000MS Memory Limit: 65536K
Total Submissions: 10878 Accepted: 5363
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
思路:簡單的二分,然而題目開始沒讀懂(英語硬傷),題目大意:有n個欄杆,c只奶牛,問怎樣使最小的距離最大.
二分距離,基本上能想到這一點就能做出來了(只要二分不寫掛).

#include <cstdio>
#include <cmath>
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
int n,c,a[100005];
bool check(int x)
{
    int t=1;
    int biao=1;
    for (int i=2;i<=n;i++)
    {
        if (a[i]-a[biao]>=x) {t++;biao=i;
        }
        if (t>=c) return true;
    }
    return false;
}
void readdata()
{
    while (~scanf("%d%d",&n,&c))
    {   
        for (int i=1;i<=n;i++)
        {
            scanf("%d",&a[i]);
        }
        sort(a,a+n);
        int l=0;
        int r=a[n]-a[1];
        while (l+1<r)
        {
            int mid=(l+r)>>1;
            if (check(mid)) l=mid;
            else r=mid;
        }
        printf("%d",l);
    }

}
int main()
{
    readdata();
}