# GeetCode Hub

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`

public String convert(String s, int numRows) { if(s==null || s.length() == 0){ return s; } int len = s.length(); StringBuilder[] sbList = new StringBuilder[numRows]; for(int i=0;i<numRows;i++){ sbList[i] = new StringBuilder(); } int i=0; while(i<len){ for(int j=0;j<numRows && i< len ; j++){ sbList[j].append(s.charAt(i)); i++; } for(int j=numRows-2;j>=1 && i<len;j--){ sbList[j].append(s.charAt(i)); i++; } } StringBuilder res = new StringBuilder(); for(i=0;i<numRows;i++){ res.append(sbList[i]); } return res.toString(); }

The main gist of this question is to get the idea of how we can use StringBuilder to append the characters at a particular level of the row. It is being explained in a detailed way in the video.
Time Complexity: O(n)  // for traversing through each character of the string.

Space Complexity: O(n)  // for storing the result in StringBuilder.