LeetCode 6 - ZigZag Conversion

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本文介绍了一种特殊的字符串转换算法——ZigZag转换。该算法将输入字符串以Z形方式分布在多行中，再按行读取形成新的字符串。以PAYPALISHIRING为例，当行数为3时，输出为PAHNAPLSIIGYIR。文中提供了一个C++实现示例。

ZigZag Conversion Dec 6 '11

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".

class Solution {
public:
    string convert(string s, int nRows) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function    
        vector<string> vs(nRows);
        int r = 0;
        bool down = true;
        for (int i = 0; i < s.length(); i++) {
            vs[r] += s[i];
            if (r == 0) {
                down = true;
            } else if (r == nRows-1) {
                down = false;
            }
            if (down && r < nRows-1) {
                r++;
            }
            if (!down && r > 0) {
                r--;
            }
        }
        
        string ret;
        for (int i = 0; i < nRows; i++) {
            ret += vs[i];
        }
        return ret;
    }
};