题目描述
把只包含质因子2、3和5的数称作丑数(Ugly Number)。例如6、8都是丑数,但14不是,因为它包含质因子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。
C++11(clang++ 3.9)
class Solution { public: int GetUglyNumber_Solution(int index) { // input check if(0 == index) return 0; vector<int> ugly(index); ugly[0] = 1; int pointer_two = 0, pointer_three = 0, pointer_five = 0; for(int i = 1; i < index; i++) { ugly[i] = min(min(2 * ugly[pointer_two], 3 * ugly[pointer_three]), 5 * ugly[pointer_five]); if(ugly[i] == 2 * ugly[pointer_two] ) pointer_two++; if(ugly[i] == 3 * ugly[pointer_three]) pointer_three++; if(ugly[i] == 5 * ugly[pointer_five] ) pointer_five++; } return ugly[index - 1]; } };