poj 2456 二分

Aggressive cows

Time Limit: 1000MS Memory Limit: 65536KTotal Submissions: 16384 Accepted: 7837

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 312849

Sample Output

3

题意：n个牛栏放c头牛，求牛之间最短距离的最大值。

分析：二分距离，c(x)：能在此距离下安排完全部牛。

#include <cstdio>#include <cstdlib>#include <iostream>#include <stack>#include <queue>#include <algorithm>#include <cstring>#include <string>#include <cmath>#include <vector>#include <bitset>#include <list>#include <sstream>#include <set>#include <functional>using namespace std;#define INF 0x3f3f3f3f#define MAX 100typedef long long ll;int n,c;int x[100001];bool C(int dis){int lx = 0,nx = lx+1;for(int i = 1;i < c; i++){while(nx < n && x[nx] < x[lx]+dis) nx++;if(nx == n) return false;lx = nx;nx = lx+1;}return true;}int main(int argc, char const* argv[]){#ifndef ONLINE_JUDGE    freopen("in.txt", "r", stdin);    freopen("out.txt", "w", stdout);#endifcin >> n >> c;for (int i = 0; i < n; i += 1) cin >> x[i];sort(x,x+n);int lb = 0,ub = INF;while(ub-lb>1){int mid = (ub+lb)/2;if(C(mid)) lb = mid;else ub = mid;}printf("%d\n",lb);return 0;}