POJ-1338（ugly number，STL-pair的应用）

 Ugly numbers are numbers whose only prime factors are 2, 3 or 5. The sequence
1, 2, 3, 4, 5, 6, 8, 9, 10, 12, ...

typedef pair<ll, int> node_type;
int main()
{
	ll result[1500];
	priority_queue<node_type, vector<node_type>, greater<node_type> >Q;
	Q.push(make_pair(1, 2));
	int i;
	for (i = 0; i < 1500; ++i) {
		node_type node = Q.top();
		Q.pop();
		switch(node.second) {
			case 2: Q.push(make_pair(node.first * 2, 2));
			case 3: Q.push(make_pair(node.first * 3, 3));
			case 5: Q.push(make_pair(node.first * 5, 5));
		}
		result[i] = node.first;
	}
	int n;
	while (cin>>n && n) {
		cout<<result[n - 1]<<endl;
	}
	return 0;
}