GETTING WA IN IITWPC4D

The problem link is : http://www.spoj.com/problems/IITWPC4D/

The solution link is : https://ideone.com/fAfVTL

I have tested my code for over 100 testcases and i found my code is working fine but still i am getting WA…

please if anyone can help me find a testcase for which my code fails… thank you



int a[100010], b[100010];
 
int main()
{
//	ios_base::sync_with_stdio(false);
	int t, n;
	cin >> t;
	set<int>::iterator it;
	set<int>::reverse_iterator it1;
	set<int> s;
	for (int cs = 1; cs <= t; cs++) {
		cout << "Test : " << cs << endl;
		s.clear();
		cin >> n;
		bool f = true;
		for (int i = 0; i < n; i++) {
			cin >> a[i];
			if (a[i] > i) {
				f = false;
			}
		}
		if (!f) {
			cout << -1 << endl;
			continue;
		}
		int x = n;
		for (int i = n - 1; i >= 0; i--) {
			if (a[i] == 0) {
				if (!s.empty()) {
					it1 = s.rbegin();
					b[i] = *it1;
					it = s.find(*it1);
					s.erase(it);
				} else {
					b[i] = x--;
				}
			} else if (s.size() == a[i]) {
				b[i] = x--;
			} else if (s.size() < a[i]) {
				int y = a[i] - s.size();
				for (int j = 0; j < y; j++) {
					s.insert(x--);
				}
				b[i] = x--;				
			} else {
				int y = s.size() - a[i];
				it = s.lower_bound(*s.begin() - 1 + y);
				b[i] = *it;
				s.erase(it);
			}
		}
		for (int i = 0; i < n; i++) {
			cout << b[i] << " ";
		}
		cout << endl;
	}
	return 0;
}

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