practice-problems

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. An input string is valid if: 1. Open brackets must be closed by the same type of brackets. 2. Open brackets must

Problem: Given an integer x, return true if x is palindrome integer. An integer is a palindrome when it reads the same backward as forward. using strings num = str(x) head = 0 tail = len(num) - 1 while head < tail: # return false if the values at head and tail

Problem: Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target. Each input has exactly one solution, and you may not use the same element twice. brute force - O(n2) time for i in range(len(