POJ2456 Aggressive cows

Description

题目

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

Analysis

以距离为主线,可以确定遍历范围,问题在于如何判断某距离合适,这里再进行二分搜索,总时间复杂度O(nlogn^2)

Code

#include<bits/stdc++.h>
using namespace std;
int a[100000];
int m,c;//space
int f(int d){
    auto x=a;
    for(int i=1;i<c;++i){
        x=lower_bound(x,a+m,*x+d);
        if(x==a+m)return 0;
    }
    return 1;
}
int main(){
    while(~scanf("%d %d",&m,&c)){
        for(int i=0;i<m;++i)scanf("%d",&a[i]);
        sort(a,a+m);
        int l=1,r=*(a+m-1)-*a+1;
        while(l<r){
            int mid=l+(r-l)/2;
            if(f(mid)==0)r=mid;
            else l=mid+1;
        }
        printf("%d\n",l-1);
    }
    return 0;
}