UVa 11621 – Small Factors

#include <iostream>
#include <cstdlib>
#include <cstdio>

using namespace std;

int next[330];

int bs(int key, int r)
{
	int l = 0,m;
	while (l < r) {
		m = (l+r)/2;
		if (next[m] < key)
			l = m+1;
		else r = m;
	}
	return r;
}

int main()
{
	int two = 0,three = 0,count = 0;
	next[0] = 1;
	while (next[count] > next[count-1]) {
		if (next[two]*2 < next[three]*3) 
			next[++ count] = next[two ++]*2;
		else {
			if (next[three]*3 == next[two]*2) two ++;
			next[++ count] = next[three ++]*3;
		}
	}
	
	int n;
	while (cin >> n && n)
		cout << next[bs(n, count)] << endl;
		
	return 0;
}