Sorting with while loops

While loops help with running code block repeatedly over a condition until failure of the condition. Sorting algorithms need to perform repeated comparisons and swapping operations over certain conditions and sometimes it becomes difficult to understand the loop start and end indexes. While loops help in exactly pointing out what indexes mean and how they are changed within the algorithm. Following are 3 common sorting algorithms which will use while loops to perform sorting:

Bubble Sort

Bubble sort’s core logic it do N-1 loops over the set of N items and on each pass move the highest element to the end of the array by comparing and swapping the neighbouring item.

Example of 1st Pass :

int[] data = {4,3,2,1}

private static void bubble(int[] data) {
        int outerStart = 0;
        int outerEnd = data.length - 1;
        int innerStart;
        int innerEnd;

        while (outerStart <= outerEnd) {
            innerStart = 1;
            innerEnd = outerEnd - outerStart;
            while (innerStart <= innerEnd) {
                if (data[innerStart] < data[innerStart - 1]) {
                    int temp = data[innerStart];
                    data[innerStart] = data[innerStart - 1];
                    data[innerStart - 1] = temp;
                }
                innerStart++;
            }
            outerStart++;
        }
    }

Insertion Sort

Insertion sort picks an element (key) and tries to find the correct index on its left subarray where the key belongs and then does the swapping. This results in less number of swappings than bubble sort.

private static void insertion(int[] data) {
        int outerStart = 1;
        int outerEnd = data.length - 1;
        while (outerStart <= outerEnd) {
            int innerStart = outerStart;
            int key = data[innerStart];
            while (innerStart > 0 && key < data[innerStart - 1]) {
                data[innerStart] = data[innerStart - 1];
                innerStart--;
            }
            data[innerStart] = key;
            outerStart++;
        }
    }

Selection Sort

Selection sort is the simplest to code, where, for every pass in the loop, index of the minimum element in the pass is found and then the item is swapped with the current loop index item.

private static void selection(int[] data) {
        int outerStart = 0;
        int outerEnd = data.length - 2;
        while (outerStart <= outerEnd) {
            int innerStart = outerStart;
            int innerEnd = data.length - 1;
            int smallIndex = innerStart;
            while (innerStart <= innerEnd) {
                if (data[innerStart] < data[smallIndex]) {
                    smallIndex = innerStart;
                }
                innerStart++;
            }
            int temp = data[outerStart];
            data[outerStart] = data[smallIndex];
            data[smallIndex] = temp;
            outerStart++;
        }
    }