264. Ugly Number II

https://leetcode.com/problems/ugly-number-ii/description/

解题思路：

1. 用动态规划：dp[i] represents the i-th number and p2, p3, p5 represents the i-th number for 2, 3, 5, respectively.

代码：
class Solution {
public int nthUglyNumber(int n) {

    if(n <= 0) return 0;
    int[] dp = new int[n + 1];
    dp[1] = 1;
    int p2 = 1, p3 = 1, p5 = 1;
    for(int i = 2; i <= n; i++){
        dp[i] = Math.min(2*dp[p2], Math.min(3*dp[p3], 5*dp[p5]));
        if(dp[i] == 2*dp[p2]) p2++;
        if(dp[i] == 3*dp[p3]) p3++;
        if(dp[i] == 5*dp[p5]) p5++;
    }
    return dp[n];
}

}