LeetCode/zig-zag-conversion/nodejs/index.js

/*
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
*/

const { assert }  = require('../../util/js'); 
/**
 * @param {string} s
 * @param {number} numRows
 * @return {string}
 */
const convert = (s, numRows) => {
  const pattern = [];
  let x = 0;
  let y = 0;
  let goingDown = true;
  for(let i = 0; i < s.length; i++){
    if (y === numRows  && goingDown) {
      y = numRows - 2;
      x++;
      goingDown = false;
    }
    if (y == -1 && !goingDown){
      y = 1;
      x++;
      goingDown = true;
    }

    if (!pattern[x]){
      pattern[x] = [];
    }
    pattern[x][y] = s[i];
    if (goingDown){
      y++;
    } else {
      y--;
    }
  }

  let col = 0;
  let output='';
  let j = 0;
  // Time complexity: O(n)
  while (j < s.length) {
    // Reset col counter to 0 if at the last col
    if (col === pattern.length) {
      col = 0;
    }
    // Remove empty cols from list then skip
    if (!pattern[col] || pattern[col].length === 0){
      pattern.splice(col, 1);
      continue;
    }

    const char = pattern[col][0];
    // Add character to output and increment char counter
    // Don't increment if character is null
    // char can be null since we were not adding elements in every index
    if (char) {
      output+=char;
      j++;
    }
    pattern[col].shift();
    col++;
  }
  return output;
};

let s, numRows;
/* Test Case 1
 * Input s = "PAYPALISHIRING", numRows = 3
 * Output: "PAHNAPLSIIGYIR"
 */

s = 'PAYPALISHIRING';
numRows = 3;
sol = 'PAHNAPLSIIGYIR';
assert(convert(s, numRows) == sol, 'Output: "PAHNAPLSIIGYIR"');

/* Test Case 2
 * Input: s = "PAYPALISHIRING", numRows = 4
 * Output: "PINALSIGYAHRPI"
 */
s =  'PAYPALISHIRING';
numRows = 4;
sol = 'PINALSIGYAHRPI';
assert(convert(s, numRows) == sol, 'Output: "PINALSIGYAHRPI"');

/* Test Case 3
 * Input: s = "AB", numRows = 1
 * Output: "AB"
 */
s =  'AB';
numRows = 1;
sol = 'AB';
assert(convert(s, numRows) == sol, 'Output: "AB"');