剑指offer 34 丑数

题目描述

把只包含因子2、3和5的数称作丑数（Ugly Number）。例如6、8都是丑数，但14不是，因为它包含因子7。 习惯上我们把1当做是第一个丑数。求按从小到大的顺序的第N个丑数。

思路

按照顺序生成丑数。把数组中每个数依次乘以2，3，5，得到的最小的数作为下一个丑数，同时记录下来下次开始遍历的index。

代码

# -*- coding:utf-8 -*-class Solution:    def GetUglyNumber_Solution(self, index):        # write code here        if index == 0:            return 0        numbers_list = [1]        two_index = 0        three_index = 0        five_index = 0        while len(numbers_list) < index:            two_number = 0            three_number = 0            five_number = 0            for i in range(two_index, len(numbers_list)):                tmp = numbers_list[i] * 2                if tmp > numbers_list[-1]:                    two_index = i                    two_number = tmp                    break            for i in range(three_index, len(numbers_list)):                tmp = numbers_list[i] * 3                if tmp > numbers_list[-1]:                    three_index = i                    three_number = tmp                    break            for i in range(five_index, len(numbers_list)):                tmp = numbers_list[i] * 5                if tmp > numbers_list[-1]:                    five_index = i                    five_number = tmp                    break            minnum = two_number            if minnum > three_number:                minnum = three_number            if minnum > five_number:                minnum = five_number            numbers_list.append(minnum)        return numbers_list[-1]