cooper的专栏

You are playing the following Nim Game with your friend: There is a heap of stones on the table, each time one of you take turns to remove 1 to 3 stones. The one who removes the last stone will be the

Given an array of integers, every element appears twice except for one. Find that single one. Note: Your algorithm should have a linear runtime complexity. Could you implement it without using e

Given a non-negative integer num, repeatedly add all its digits until the result has only one digit. For example: Given num = 38, the process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has only

Given a binary tree, find its maximum depth. The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. 这个就是递归，不想太多 /**  * Definitio

Invert a binary tree.      4    /   \   2     7  / \   / \ 1   3 6   9 to      4    /   \   7     2  / \   / \ 9   6 3   1 懒人就是交换递归 /**  * Definition for a binary tree node.  * stru