思路：

https://leetcode-cn.com/problems/ugly-number/solution/chou-shu-by-leetcode-solution-fazd/

代码：

class Solution {
public:
    int GetUglyNumber_Solution(int index) {
        int n = index;
        vector<int> dp(n + 1);
        dp[1] = 1;
        int p2 = 1, p3 = 1, p5 = 1;
        for (int i = 2; i <= n; i++) {
            int num2 = dp[p2] * 2, num3 = dp[p3] * 3, num5 = dp[p5] * 5;
            dp[i] = min(min(num2, num3), num5);
            if (dp[i] == num2) {
                p2++;
            }
            if (dp[i] == num3) {
                p3++;
            }
            if (dp[i] == num5) {
                p5++;
            }
        }
        return dp[n];
    }
};