6. ZigZag Conversion

/**
 * @param {string} s
 * @param {number} numRows
 * @return {string}
 */

var convert = function (s, numRows) {
	if (numRows <= 1) return s
	let i = 0,
		col = 0,
		row = 0,
		res = ''
	const len = s.length,
		zigzag = []

	for (let j = 0; j < numRows; j++) {
		zigzag.push([])
	}

	while (i < len) {
		while (row < numRows && i < len) {
			zigzag[row][col] = s[i]
			i++
			row++
		}
		row--
		while (row > 0 && i < len) {
			col++
			row--
			zigzag[row][col] = s[i]
			i++
		}
		row++
	}

	zigzag.forEach((row) => {
		row.forEach((letter) => {
			if (letter) res += letter
		})
	})

	return res
}

//Test cases
console.log(convert('hellonooby', 3))

//Time complexity - O(N) where N is the length of the string
//space complexity - size of the matrix + length of the res string
/* 
h - number of rows
N/h
*/