leetcode: ZigZag Conversion

http://oj.leetcode.com/problems/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".

思路：

也许有更好的做法，但是最简单的方法就是先一层层的输出，最后重新拼成一个字符串。

class Solution {
public:
    string convert(string s, int nRows) {
        if (1 == nRows) {
            return s;
        }

        string result;
        vector<string> rows(nRows);
        int row = 0, i = 0;
        bool down = true;
        
        while (i < s.length()) {
            rows[row].push_back(s[i]);
            ++i;
            
            if (0 == row) {
                down = true;
            }
            else if ((nRows - 1) == row) {
                down = false;
            }

            if (down) {
                ++row;
            }
            else {
                --row;
            }
        }
        
        for (row = 0; row < nRows; ++row) {
            result += rows[row];
        }
        
        return result;
    }
};