Ugly Number II问题及解法

问题描述：

Write a program to find the n-th ugly number.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first 10 ugly numbers.

Note that 1 is typically treated as an ugly number, and n does not exceed 1690.

问题分析：

本题分析与Super Ugly Number一样，这里就不多说了,详戳http://blog.csdn.net/u011809767/article/details/78351462

过程详见代码：

class Solution {public:    int nthUglyNumber(int n) {        vector<int> dp(n, INT_MAX), p{2,3,5},idx(3,0);dp[0] = 1;for (int i = 1; i < n; i++){for (int j = 0; j < 3; j++){dp[i] = min(dp[i], dp[idx[j]] * p[j]);}for (int j = 0; j < 3; j++){while (dp[idx[j]] * p[j] <= dp[i]) idx[j]++;}}return dp[n - 1];    }};