[剑指offer] 33. 丑数

class Solution
{
  public:
    int GetUglyNumber_Solution(int index)
    {
        if (index < 7)
            return index;
        vector<int> res(index);
        res[0] = 1;
        int in2 = 0, in5 = 0, in3 = 0;
        for (int i = 1; i < index; i++)
        {
            res[i] = min(res[in2] * 2, min(res[in3] * 3, res[in5] * 5));
            if (res[i] == res[in2] * 2)
                in2++;
            if (res[i] == res[in3] * 3)
                in3++;
            if (res[i] == res[in5] * 5)
                in5++;
        }
        return res[index - 1];
    }
};