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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"

class Solution {
    public String convert(String s, int numRows) {
        if(numRows == 1) {
            return s;
        }
        
        int pointer = 0;
        int row = 0; 
       
        boolean flag = false;
        List<StringBuilder> arr = new ArrayList<>();
        for(int i = 0; i < numRows; i++){
            arr.add(new StringBuilder());
        }

        while(pointer < s.length()){
            if(row < numRows){
                arr.get(row).append(s.charAt(pointer));
                pointer++;
            }
            
            if(row == 0){
                flag = true;
            }
            if(row == numRows - 1){
                flag = false;
            }
            if(flag){
                row++;  
            } else {
                row--;
            }
            
        }

        StringBuilder sb = new StringBuilder();
        for(int i = 0; i < numRows; i ++){
            sb.append(arr.get(i));
        }
        return sb.toString();
    }
}