花花酱 LeetCode 1447. Simplified Fractions

Given an integer n, return a list of all simplified fractions between 0 and 1 (exclusive) such that the denominator is less-than-or-equal-to n. The fractions can be in any order.

Example 1:

Input: n = 2
Output: ["1/2"]
Explanation: "1/2" is the only unique fraction with a denominator less-than-or-equal-to 2.

Example 2:

Input: n = 3
Output: ["1/2","1/3","2/3"]

Example 3:

Input: n = 4
Output: ["1/2","1/3","1/4","2/3","3/4"]
Explanation: "2/4" is not a simplified fraction because it can be simplified to "1/2".

Example 4:

Input: n = 1
Output: []

Constraints:

• 1 <= n <= 100

Solution: GCD

if gcd(a, b) == 1 then a/b is a simplified frication.

std::gcd is available since c++17.

Time complexity: O(n^2logn)
Space complexity: O(1)