LeetCode OJ：ZigZag Conversion（字符串的Z字型转换）

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".

将字符进行Z字型转换，然后进行存储，一开始没有想到什么好方法，看了下别人的实现，可以做的比较简单，每一行用一个字符串记录下来之后，然后拼接起来就可以，非满列字符串是有规律的，具体见下代码：

class Solution {
public:
    string convert(string s, int numRows) {
        vector<string> res;
        res.resize(numRows);
        string ret;
        int gap = numRows - 2;
        int i = 0, j;
        while(i < s.size()){
            for(j = 0; i < s.size() && j < numRows; ++i, ++j)
                res[j] += s[i];
            for(j = gap; i < s.size() && j > 0; ++i, --j)
                res[j] += s[i];
        }
        for(int k = 0; k < numRows; ++k){
            ret += res[k];
        }
        return ret;
    }
};