0006 - ZigZag Conversion

0006 - 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);

Examples

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

Input: s = "PAYPALISHIRING", numRows = 4 Output: "PINALSIGYAHRPI" Explanation:

P I N

A L S I G

Y A H R

P I

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

Java Solution

class Solution {
    
    public String convert(String s, int numRows) {
        if(numRows == 1) return s;
        
        List<StringBuilder> rows = new ArrayList<>();
        
        for(int i = 0; i < Math.min(numRows, s.length()); i++)
            rows.add(new StringBuilder());
            
        int currentRow = 0;
        boolean goingDown = false;
        
        for(char c : s.toCharArray()) {
            rows.get(currentRow).append(c);
            if(currentRow == numRows-1 || currentRow == 0) goingDown = !goingDown;
            currentRow += goingDown ? 1 : -1;
        }

        StringBuilder result = new StringBuilder();
        for(StringBuilder row : rows) result.append(row);
        
        return result.toString();
        
    }
}