Haemin Park | DS & A

Question & Examples

Start looping from with a variable called i from the end of the array towrads the beginning. Start an inner loop with a variable called j from the beginning until i - 1. If arr[j] is greater than arr[j+1], swap those two values. Return the sorted array.

// Examples
bubbleSort([3, 6, 1, 34, 65, 26, 12, 53])
 
// [1, 3, 6, 12, 26, 34, 53, 65]

Implementation

function bubbleSort(arr) {
  for (i = arr.length; i > 0; i--) { // 1
    for (j = 0; j < i - 1; j++) { // 2
      if (arr[j] > arr[j + 1]) { // 3
        [arr[j], arr[j + 1]] = [arr[j + 1], arr[j]] // 4
      }
    }
  }
  return arr
}

start a for loop. Set i to arr.length so it starts from the end of the array.
start another for loop. Set j to i - 1. We do this so we decrement the amount of times each pairs are being compared.
check to see if the element on the left is bigger than that on the right.
If so, swap those elements

We can make this more intuitive by console logging some values

function bubbleSort(arr) {
  for (i = arr.length; i > 0; i--) { // 1
    for (j = 0; j < i - 1; j++) { // 2
    console.log(arr, arr[j], arr[j+1])
      if (arr[j] > arr[j + 1]) { // 3
        [arr[j], arr[j + 1]] = [arr[j + 1], arr[j]] // 4
      }
    }
    console.log("ONE LOOP FINISHED!")
  }
  return arr
}
 
console.log(bubbleSort([3, 6, 1, 34, 65, 26, 12, 53]))
 
// [3, 6, 1, 34, 65, 26, 12, 53] 3 6
// [3, 6, 1, 34, 65, 26, 12, 53] 6 1
// [3, 1, 6, 34, 65, 26, 12, 53] 6 34
// [3, 1, 6, 34, 65, 26, 12, 53] 34 65
// [3, 1, 6, 34, 65, 26, 12, 53] 65 26
// [3, 1, 6, 34, 26, 65, 12, 53] 65 12
// [3, 1, 6, 34, 26, 12, 65, 53] 65 53
// ONE LOOP FINISHED!
// [3, 1, 6, 34, 26, 12, 53, 65] 3 1
// [1, 3, 6, 34, 26, 12, 53, 65] 3 6
// [1, 3, 6, 34, 26, 12, 53, 65] 6 34
// [1, 3, 6, 34, 26, 12, 53, 65] 34 26
// [1, 3, 6, 26, 34, 12, 53, 65] 34 12
// [1, 3, 6, 26, 12, 34, 53, 65] 34 53
// ONE LOOP FINISHED!
// [1, 3, 6, 26, 12, 34, 53, 65] 1 3
// [1, 3, 6, 26, 12, 34, 53, 65] 3 6
// [1, 3, 6, 26, 12, 34, 53, 65] 6 26
// [1, 3, 6, 26, 12, 34, 53, 65] 26 12
// [1, 3, 6, 12, 26, 34, 53, 65] 26 34
// ONE LOOP FINISHED!
// [1, 3, 6, 12, 26, 34, 53, 65] 1 3
// [1, 3, 6, 12, 26, 34, 53, 65] 3 6
// [1, 3, 6, 12, 26, 34, 53, 65] 6 12
// [1, 3, 6, 12, 26, 34, 53, 65] 12 26
// ONE LOOP FINISHED!
// [1, 3, 6, 12, 26, 34, 53, 65] 1 3
// [1, 3, 6, 12, 26, 34, 53, 65] 3 6
// [1, 3, 6, 12, 26, 34, 53, 65] 6 12
// ONE LOOP FINISHED!
// [1, 3, 6, 12, 26, 34, 53, 65] 1 3
// [1, 3, 6, 12, 26, 34, 53, 65] 3 6
// ONE LOOP FINISHED!
// [1, 3, 6, 12, 26, 34, 53, 65] 1 3
// ONE LOOP FINISHED!
// [1, 3, 6, 12, 26, 34, 53, 65]

As we can see above, the number of times the pairs(arr[j] and arr[j+1]) are being compared decrements by one.

Bubble sort basics

Question & Examples

Implementation