摘要：
Invert a binary tree. 4 / \ 2 7 / \ / \ 1 3 6 9 to 4 / \ 7 2 / \ / \ 9 6 3 1 Trivia: This problem was inspired by this original tweet by Max Howell: G 阅读全文
摘要：
Given two words word1 and word2, find the minimum number of steps required to make word1 and word2 the same, where in each step you can delete one cha 阅读全文
摘要：
Given n processes, each process has a unique PID (process id) and its PPID (parent process id). Each process only has one parent process, but may have 阅读全文