# leetcode

LeetCode problem solving notes. Given an integer num, repeatedly add all its digits until the result has only one digit, and return it.

LeetCode problem solving notes. Given the root of a binary tree, return all root-to-leaf paths in any order.

LeetCode problem solving notes. Given the root of a binary tree, return the postorder traversal of its nodes' values.

LeetCode problem solving notes. You have a long flowerbed in which some of the plots are planted, and some are not. However, flowers cannot be planted in adjacent plots.

LeetCode problem solving notes. Write a SQL query for a report that provides the following information for each person in the Person table, regardless if there is an address for each of those people.

LeetCode problem solving notes. Given an integer array nums and an integer k, return true if there are two distinct indices i and j in the array such that nums[i] == nums[j] and abs(i - j) <= k.

LeetCode problem solving notes. Given a non-empty array of integers nums, every element appears twice except for one. Find that single one.

LeetCode problem solving notes. Given the head pointer of the singly linked list and the value of a node to be deleted, define a function to delete the node.

LeetCode problem solving notes. Given a string columnTitle that represents the column title as appear in an Excel sheet, return its corresponding column number.

LeetCode problem solving notes. Given an integer columnNumber, return its corresponding column title as it appears in an Excel sheet.