点击打开题目
C. Counting Kangaroos is Fun
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output
There are n kangaroos with pockets. Each kangaroo has a size (integer number). A kangaroo can go into another kangaroo's pocket if and only 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.
Input
The 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).
Output
Output a single integer — the optimal number of visible kangaroos.
Examples
input
8
2
5
7
6
9
8
4
2
output
5
input
8
9
1
6
2
6
5
8
3
output
5
在 0 和 n/2 之间对能干掉的人数二分。
代码如下:
#include <cstdio>
#include <algorithm>
using namespace std;
int num[500000+11];
int n;
bool check(int x)
{
int pos = x - 1;
for (int i = 0 ; i < x ; i++)
{
pos = lower_bound (num + pos + 1 , num + n , 2*num[i]) - num;
if (pos == n)
return false;
}
return true;
}
int main()
{
while (~scanf ("%d",&n))
{
for (int i = 0 ; i < n ; i++)
scanf ("%d",&num[i]);
sort(num , num + n);
int l = 0;
int r = n / 2 + 1;
int mid;
while (r >= l)
{
mid = (l + r) >> 1;
if (check(mid))
l = mid + 1;
else
r = mid - 1;
}
printf ("%d\n",n-r);
}
return 0;
}