1. Two Sum

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,

return [0, 1].

UPDATE (2016/2/13):
The return format had been changed to zero-based indices. Please read the above updated description carefully.

注：给出一个整数向量，和一个目标值，找出向量中加和等于目标值的那两个数所在的位置。（假如只有一组解） （位置索引是从0开始）

6. ZigZag Conversion

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 I I G

Y   I   R

And then read line by line: "PAHNAPLSIIGYIR"

Write the code that will take a string and make this conversion given a number of rows:

string convert(string text, int nRows);

convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".

注：把一串字母按照"z"形排列，现在要按行读出来。（不懂）

查了一下是这个样子：text="PAYPALISHIRING" , nRows=4 时

P     I    N

A   L S  I G

Y A   H R

P     I

结果是 "PINALSIGYAHRPI".

要弄清楚规律，按列存储一个字符串，然后按行读出来