https://leetcode.com/problems/zigzag-conversion/

problems-zigzag-conversion.ts

function convert(s: string, numRows: number): string {
    const chars = Array.from(s);
    const rows: string[][] = [];
    const I = 2;

    chars.forEach((char, index) => {
        const factor = (numRows * 2 - I) || 1;
        const cycle = Math.floor(index / factor);
        const phase = index - factor * cycle;
        const isDiagonal = phase > (numRows - 1);

        if (!isDiagonal) {
            rows[phase] = rows[phase] || [];
            rows[phase].push(char)
        } else {
            const diagonalPhase = phase - (numRows - 1);
            rows[numRows - 1 - diagonalPhase].push(char);
        }
    })

    return rows.map(r => r.join("")).join("");
}