LeetCode – Strings – Make String Great
Given a string s of lower and upper case English letters. A good string is a string which doesn’t have two adjacent characters s and s where: To make the…
LeetCode – Strings – Path Crossing
Given a string path, where path = 'N', 'S', 'E' or 'W', each representing moving one unit north, south, east, or west, respectively. You start at the origin (0, 0)…
LeetCode – Strings – Reformat Date
Given a date string in the form Day Month Year, where: Convert the date string to the format YYYY-MM-DD, where: Example 1: Input: date = "20th Oct 2052" Output: "2052-10-20"…
LeetCode – Arrays – Last Stone Weight
We have a collection of stones, each stone has a positive integer weight. Each turn, we choose the two heaviest stones and smash them together. Suppose the stones have weights…
LeetCode – Arrays – Next Greater Element I
You are given two arrays (without duplicates) nums1 and nums2 where nums1’s elements are subset of nums2. Find all the next greater numbers for nums1‘s elements in the corresponding places…
LeetCode – Stack – Remove All Adjacent Duplicates In String
Given a string S of lowercase letters, a duplicate removal consists of choosing two adjacent and equal letters, and removing them. We repeatedly make duplicate removals on S until we…
LeetCode – Stack – Build an Array With Stack Operations
Given an array target and an integer n. In each iteration, you will read a number from list = {1,2,3..., n}. Build the target array using the following operations: You…
LeetCode – Stack – Remove Outermost Parentheses
Given an array target and an integer n. In each iteration, you will read a number from list = {1,2,3..., n}. Build the target array using the following operations: You…
LeetCode – Stack – Remove Outermost Parentheses
A valid parentheses string is either empty (""), "(" + A + ")", or A + B, where A and B are valid parentheses strings, and + represents string concatenation.…
LeetCode – Hashtable – Number of Good Pairs
Given an array of integers nums. A pair (i,j) is called good if nums == nums and i < j. Return the number of good pairs. Example 1: Input: nums…