19. Jolly Jumpers

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
	int n;
	cin >> n;

	vector<int> Temp(n);
	vector<bool> Res(n);
	int Pos = 0;

	for (int i = 0; i < n; ++i)
	{
		cin >> Temp[i];
	}

	for (int i = 1; i < n; ++i)
	{
		if (Temp[i - 1] - Temp[i] > 0)
		{
			Res[Temp[i - 1] - Temp[i]] = true;
		}
		else if(Temp[i - 1] - Temp[i] < 0)
		{
			Res[-(Temp[i - 1] - Temp[i])] = true;
		}
	}

	for (int i = 1; i < Res.size(); ++i)
	{
		if (Res[i] == false)
		{
			cout << "NO" << endl;
			return 0;
		}
	}

	cout << "YES" << endl;
}