LeetCode 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" .

题意：给你个按N型排列的字符串，并告诉你几行，让你输出每一行连起来的字符串

思路：首先画出N行，借用一张图

通过这张图得出每相邻偶数行的坐标差，和相邻的坐标差，计算就行了

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

        string ans = "";
        int len = s.length();
        for (int i = 0; i < nRows; i++) {
            int cur = i;
            while (cur < len) {
                ans += s[cur];
                if (i != 0 && i != nRows-1 && (cur + 2 * (nRows - 1 - i)) < len) 
                    ans += s[cur + 2 * (nRows- 1 - i)];
                cur += 2 * (nRows - 1); 
            }
        }

        return ans;
    }
};