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

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

string convert(string text, int nRows);

題意：給你個按N型排列的字符串，並告訴你幾行，讓你輸出每一行連起來的字符串

通過這張圖得出每相鄰偶數行的坐標差，和相鄰的坐標差，計算就行了

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;
    }
};