Zigzag Conversion

Leetcode Problem 6: Zigzag Conversion

Problem Summary

Given a string s and a number of rows numRows, rearrange its characters by writing them in a zigzag pattern across numRows rows, then read the result back row by row to produce the output string.

Characters are placed diagonally top-to-bottom filling each row, then diagonally bottom-to-top, and this repeats until all characters are placed. For example, "PAYPALISHIRING" written with 3 rows looks like this:

P   A   H   N
A P L S I I G
Y   I   R

And then read line by line: "PAHNAPLSIIGYIR"

Write a function convert(s, numRows) that performs this transformation and returns the resulting string.

• The string length is between 1 and 1,000 characters.
• The string may contain uppercase and lowercase English letters, commas (,), and periods (.).
• The number of rows is between 1 and 1,000.

Techniques

• String

Solution

function convert(s: string, numRows: number): string {
    if (numRows === 1) {
        return s
    }

    let zigZagStrings: string[] = Array(numRows).fill('')
    let currentArrayIndex = 0
    let direction: 1 | -1 = 1

    for (let i = 1; i <= s.length; i++) {
        zigZagStrings[currentArrayIndex] = zigZagStrings[currentArrayIndex] + s.charAt(i - 1)

        if (currentArrayIndex === 0) {
            direction = 1
        }

        if (currentArrayIndex === numRows - 1) {
            direction = -1
        }

        currentArrayIndex += direction
    }

    return zigZagStrings.join('')
}

console.log(convert("PAYPALISHIRING", 3))