coderforces 372A Counting Kangaroos is Fun（二分）

A. Counting Kangaroos is Funtime limit per test1 secondmemory limit per test256 megabytesinputstandard inputoutputstandard outputThere are n kangaroos with pockets. Each kangaroo has a size (integer number). A kangaroo can go into another kangaroo's pocket if andonly if the size of kangaroo who hold the kangaroo is at least twice as large as the size of kangaroo who is held.Each kangaroo can hold at most one kangaroo, and the kangaroo who is held by another kangaroo cannot hold any kangaroos.The kangaroo who is held by another kangaroo cannot be visible from outside. Please, find a plan of holding kangaroos with the minimal number of kangaroos who is visible.InputThe first line contains a single integer — n (1 ≤ n ≤ 5·105).Each of the next n lines contains an integer si —the size of the i-th kangaroo(1 ≤ si ≤ 105).OutputOutput a single integer — the optimal number of visible kangaroos.Examplesinput

8
2
5
7
6
9
8
4
2

output

5

input

891626583

output

5

题意：有N个袋鼠每个袋鼠的口袋里可以放一只体重小于其体重的小于它二分之一重量的袋鼠现在将一些袋鼠放进其它的袋鼠口袋里问最多能见到多少袋鼠。

#include<cstdio>#include<iostream>#include<algorithm>using namespace std;const int maxn = 500010;int n;int a[maxn];bool judge(int mid){if(mid < (n + 1) / 2) return false;for(int i = mid + 1 ; i <= n ; i++)if(a[i] * 2 > a[i-mid]) return false;return tr4000ue;}bool cmp(int a , int b){return a > b;}int main(){scanf("%d",&n);for(int i = 1 ; i <= n ; i++)scanf("%d",&a[i]);sort(a+1,a+n+1,cmp);int l = 1  , r = n ,ans;while( l <= r){int mid = (l + r) / 2;if(judge(mid)){ans = mid;r = mid - 1;}elsel = mid + 1;}printf("%d\n",ans);return 0;}