Sorting

Bubble Sort

Repeatedly walk the array comparing adjacent pairs and swapping any that are out of order. After pass k, the k largest elements are in their final positions at the end. Early-exit when a pass makes zero swaps.

Algorithm

Canonical input from the lesson spec is [5, 1, 4, 2, 8]. Three passes sort the array; pass three triggers the early exit.

Basic Implementation

basic.dart 
void main() {
  final arr = <int>[5, 1, 4, 2, 8];
  final n = arr.length;
  for (var i = 0; i < n - 1; i++) {
    var swapped = false;
    for (var j = 0; j < n - i - 1; j++) {
      if (arr[j] > arr[j + 1]) {
        final tmp = arr[j];
        arr[j] = arr[j + 1];
        arr[j + 1] = tmp;
        swapped = true;
      }
    }
    if (!swapped) {
      break;
    }
  }
  print(arr);
}

Complexity

  • Time: O(n^2) worst and average, O(n) best with early exit
  • Space: O(1)
  • Stable: yes

Implementation notes

  • Dart: write the two explicit loops and the swapped flag. Do not call arr.sort(); it would hide the comparison-and-swap mechanics the lesson is teaching.
  • The replay shows the compared pair on each frame and the post-swap array, matching the lesson spec's per-pass tables.
adjacent swap Swap neighbouring out-of-order pairs.
early termination A pass with zero swaps means the array is already sorted.