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

var convert = function(s, numRows) {
  if (numRows === 1){
    return s;
  }
  
  let output = "";
  let n = s.length;
  let cycleLen = 2 * numRows - 2;
  
  for (let i = 0; i < numRows; i++){
    for (let j = 0; j + i < n; j += cycleLen) {
      output += s.charAt(j+i);
      if (i !== 0 && i !== numRows-1 && j + cycleLen - i < n){
        output += s.charAt(j + cycleLen -i);
      }
    }
  }
  
  return output;
};