摘要：
Write a function that reverses a string. The input string is given as an array of characters char[]. Do not allocate extra space for another array, yo 阅读全文
摘要：
Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum. N 阅读全文
摘要：
Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree [1,2,2,3,4,4,3] is symmet 阅读全文