[Leetcode] #263#264 Ugly Number I & II

Discription:

Write a program to check whether a given number is an ugly number.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 are ugly while14 is not ugly since it includes another prime factor 7.

Note that 1 is typically treated as an ugly number.

Solution:

bool isUgly(int num) {while (num % 2 == 0 && num)num /= 2;while (num % 3 == 0 && num)num /= 3;while (num % 5 == 0 && num)num /= 5;return num == 1;}

Discription:

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.

Solution:

int nthUglyNumber(int n) {vector<int> res(n, 0);res[0] = 1;int index2 = 0, index3 = 0, index5 = 0;for (int i = 1; i < n; i++){int temp = min(res[index2] * 2, res[index3] * 3);temp = min(temp, res[index5] * 5);res[i] = temp;                      //注意等号while (res[index2] * 2 <= res[i])   //(res[index2] * 2 == res[i]) index2++;while (res[index3] * 3 <= res[i])   //(res[index3] * 3 == res[i])index3++;while (res[index5] * 5 <= res[i])   //(res[index5] * 5 == res[i])index5++;}return res[n - 1];}