204. Count Primes

Given an integer n, return the number of prime numbers that are strictly less than n.

Example 1:

Input: n = 10
Output: 4
Explanation: There are 4 prime numbers less than 10, they are 2, 3, 5, 7.

84. Largest Rectangle in Histogram

Given an array of integers heights representing the histogram's bar height where the width of each…