摘要：
In a deck of cards, every card has a unique integer. You can order the deck in any order you want. Initially, all the cards start face down (unreveale 阅读全文
摘要：
For a binary tree T, we can define a flip operation as follows: choose any node, and swap the left and right child subtrees. A binary tree X is flip e 阅读全文
摘要：
Given an array of 4 digits, return the largest 24 hour time that can be made. The smallest 24 hour time is 00:00, and the largest is 23:59. Starting f 阅读全文