我们把只包含质因子 2、3 和 5 的数称作丑数（Ugly Number）。求按从小到大的顺序的第 n 个丑数。

示例:

输入: n = 10
输出: 12
解释: 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 是前 10 个丑数。
1
2
3
说明:

1 是丑数。
n 不超过1690。

class Solution {public int nthUglyNumber(int n) {int[] dp = new int[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] = Math.min(Math.min(num2, num3), num5);if (dp[i] == num2) {p2++;}if (dp[i] == num3) {p3++;}if (dp[i] == num5) {p5++;}}return dp[n];}
}

class Solution {public int nthUglyNumber(int n) {if(n<=0){return 0;}int[] dp = new int[n];dp[0] = 1;int a = 0, b = 0, c = 0;int i = 1;while(i<n){dp[i] = Math.min(Math.min(dp[a]*2, dp[b]*3), dp[c]*5);while(dp[a]*2<=dp[i]){a++;}while(dp[b]*3<=dp[i]){b++;}while(dp[c]*5<=dp[i]){c++;}i++;}return dp[n-1];}
}