Robina Li

Given a 2D integer array nums, return all elements of nums in diagonal order.

Given the head of a singly linked list, reverse the list, and return the reversed list.

Design a data structure that follows the constraints of a Least Recently Used (LRU) cache.

A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros.

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 Java for expression evaluation with +, −, ×, ÷ and parentheses. See also Stack for RPN and nested expressions. Contents Basic Calculator (+, -, parentheses) Basic Calculator II...

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.