s0006_zigzag_conversion

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

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

Solution

/**
 * @param {string} s
 * @param {number} numRows
 * @return {string}
 */
var convert = function (s, numRows) {
    const sLen = s.length
    if (numRows === 1) {
        return s
    }
    const maxDist = numRows * 2 - 2
    let result = ''

    for (let i = 0; i < numRows; i++) {
        let index = i
        if (i === 0 || i === numRows - 1) {
            while (index < sLen) {
                result += s[index]
                index += maxDist
            }
        } else {
            while (index < sLen) {
                result += s[index]
                index += maxDist - i * 2
                if (index >= sLen) {
                    break
                }
                result += s[index]
                index += i * 2
            }
        }
    }
    return result
}

export { convert }