1117. Eddington Number(25)

#include <iostream>
#include <algorithm>

using namespace std;

int num[100010];

int getindex(int low, int high, int goal)
{
	int mid;
	while(low < high)
	{
		mid = (low + high) / 2;
		if(num[mid] > goal)
		{
			high = mid;
		}
		else
		{
			low = mid + 1;
		}
	}

	return high;
}

int main()
{
	int n;
	scanf("%d", &n);

	int i;
	for(i = 1; i <= n; i++)
	{
		scanf("%d", &num[i]);
	}

	sort(num + 1, num + n + 1);

	int index, count;
	for(i = n; i >= 0; i--)
	{
		index = getindex(1, n + 1, i);
		count = n + 1 - index;

		if(count >= i)
		{
			break;
		}
	}

	printf("%d\n", i);

	system("pause");
	return 0;
}