# largestNum holds the largest number of each subarray. If the subarray index is larger than the largestNumber index,
# loop through until the largest and store it.

function largestOfFour(arr) {
  var largestNum = [0,0,0,0];
  for(var i = 0; i< arr.length;i++){
    for(var j = 0; j < arr[i].length;j++){
      if(largestNum[i] < arr[i][j]){
        largestNum[i] = arr[i][j];
      }
    }
  }
  return largestNum;
}

largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);