PAT A1117 Eddington Number (25point(s))

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British astronomer Eddington liked to ride a bike. It is said that in order to show off his skill, he has even defined an "Eddington number", E -- that is, the maximum integer E such that it is for E days that one rides more than E miles. Eddington's own E was 87.

Now given everyday's distances that one rides for N days, you are supposed to find the corresponding E (≤N).

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤$10^5$), the days of continuous riding. Then N non-negative integers are given in the next line, being the riding distances of everyday.

Output Specification:

For each case, print in a line the Eddington number for these N days.

Sample Input:

10
6 7 6 9 3 10 8 2 7 8

Sample Output:

6

解答

#include<iostream>
#include<algorithm>
#include<vector>

using namespace std;

int main()
{
	int num, i;
	cin >> num;
	vector<int> arr(num, 0);
	for (i = 0; i < num; i++) 
		cin >> arr[i];
	sort(arr.begin(), arr.end(), greater<int>());
	for (i = 0; i < num; i++) {
		if (i + 1 >= arr[i]) break;
	}
	cout << i;
	return 0;
}