yoruru的努力日記

1472. Design Browser History

You have a browser of one tab where you start on the homepage and you can visit another url, get back in the history number of steps or move forward in the history number of steps.

20. Valid Parentheses

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

227. Basic Calculator II

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

150. Evaluate Reverse Polish Notation

You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation.

232. Implement Queue using Stacks

Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push, peek, pop, and empty).

54. Spiral Matrix

Given an m x n matrix, return all elements of the matrix in spiral order.

543. Diameter of Binary Tree

Given the root of a binary tree, return the length of the diameter of the tree.

104. Maximum Depth of Binary Tree

Given the root of a binary tree, return its maximum depth.

155. Min Stack

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

122. Best Time to Buy and Sell Stock II

You are given an integer array prices where prices[i] is the price of a given stock on the ith day.