Lesson 38: The Insertion Sort Algorithm

Insertion sort iterates, consuming one input element each repetition, and growing a sorted output list. At each iteration, insertion sort removes one element from the input data, finds the location it belongs within the sorted list, and inserts it there. It repeats until no input elements remain.

Characteristics

• In-place algorithm
• It will take 100 steps to sort 10 items, 10000 steps to sort 100 items, 1000000 steps to sort 1000 items
• Stable algorithm

Time complexity

Worst-case performance: О(n²) comparisons and swaps
Best-case performance: O(n) comparisons, O(1) swaps
Average performance: О(n²) comparisons and swaps
Worst-case space complexity: О(n) total, O(1) auxiliary

Implementation

static int[] sort(final int[] in) {
    for (var firstUnsortedIndex = 1; firstUnsortedIndex < in.length; firstUnsortedIndex++) {
        int i;
        var newElement = in[firstUnsortedIndex];
        for (i = firstUnsortedIndex; i > 0 && in[i - 1] > newElement; i--) {
            in[i] = in[i - 1];
        }

        in[i] = newElement;
    }

    return in;
}

Links

• Insertion Sort Algorithm

Source Code

akarazhev/algorithms-structures-patterns