Robina Li

Design and implement a data structure for a Least Frequently Used (LFU) cache.

The stack is one of the most versatile data structures in coding interviews. Whether you’re matching parentheses, evaluating expressions, or finding the next greater element in an array, a stack...

Minimal, copy-paste Python for expression evaluation with +, −, ×, ÷ and parentheses. See also Stack for RPN and nested expressions.

Given a string s representing a valid expression, implement a basic calculator to evaluate it, and return the result of the evaluation.

Implement a basic calculator to evaluate a simple expression string.

Given a string s which represents an expression, evaluate this expression and return its value.

Rearrange nums such that nums[0] < nums[1] > nums[2] < nums[3] ... (wiggle order).

A parentheses string is valid if and only if:

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

Given a binary array nums, return the maximum length of a contiguous subarray with an equal number of 0 and 1.