档案日期2015的32

题目描述：

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 one digit, return ...

题目描述：

Given a binary tree, return all root-to-leaf paths.

For example, given the following binary tree:

   1
 /   \
2     3
 \
  5

All root-to-leaf paths are:

["1->2->5", "1->3"]

题目大意：

给定一棵二叉树，返回所有“根到叶子”的路径。

例如，给定下面的二叉树：

   1
 /   \
2     3
 \
  5

所有“根到叶子”路径为：

["1->2->5", "1->3"]

解题思路：

树的遍历 ...

题目描述：

A city's skyline is the outer contour of the silhouette formed by all the buildings in that city when viewed from a distance. Now suppose you are given the locations and height of all the buildings as shown on ...

让我们通过考虑下面的问题来理解线段树。

给定一个数组arr[0 . . . n-1]，我们要对数组执行这样的操作：

1 计算从下标l到r的元素之和，其中 0 <= l <= r <= n-1
​2 修改数组指定元素的值arr[i] = x，其中 0 <= i <= n-1

一个简单的方案是从l到r执行循环，计算给定区间的元素之和。更新值的时候，简单地令arr[i] = x。第一个操作花费O(n)的时间，第二个操作花费O ...

题目描述：

The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

P   A   H   N
A P L S ...