6

6. ZigZag Conversion (Medium)

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

Related Topics:
String

Solution 1.

// OJ: https://leetcode.com/problems/zigzag-conversion/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    string convert(string s, int numRows) {
        if (numRows == 1) return s;
        int N = s.size(), d = (numRows - 1) * 2;
        string ans;
        for (int i = 0; i < numRows; ++i) {
            int w = 2 * i; 
            for (int j = i; j < N;) {
                ans += s[j];
                w = d - w;
                if (!w) w = d;
                j += w;
            }
        }
        return ans;
    }
};