[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 s, int numRows);

 

Example 1:

Input: s = "PAYPALISHIRING", numRows = 3 Output: "PAHNAPLSIIGYIR"

Example 2:

Input: s = "PAYPALISHIRING", numRows = 4 Output: "PINALSIGYAHRPI" Explanation: P I N A L S I G Y A H R P I

Example 3:

Input: s = "A", numRows = 1 Output: "A"

 

Constraints:

• 1 <= s.length <= 1000
• s consists of English letters (lower-case and upper-case), ',' and '.'.
• 1 <= numRows <= 1000

class Solution {
public:
    string convert(string s, int numRows) {
        string ans = "";
        int step = (numRows + (numRows - 2));
        int loops = step < 1 ? 1 : (int)ceil((double)s.length() / (double)step);
        int cur = 0, start, end;
        while (ans.length() < s.length())
        {
            for (int i = 0; i < loops; i++)
            {
                start = (step * i) + cur;
                if (cur == 0)
                {
                    if (start < s.length()) ans += s[start];
                }
                else
                {
                    end = (step + (step * i)) - cur;
                    if (start < s.length()) ans += s[start];
                    if (end < s.length() && end > start) ans += s[end];
                }
            }
            cur++;
        }
        return ans;
    }
};