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package chimomo.learning.java.algorithm.sort;

/**
 * @author Chimomo
 *
 * <p>
 * Bubble sort is a kind of simple sort algorithm in computer science. It
 * repeatedly visit the sequence to be sorted, compare two elements each time,
 * swap them if their order is wrong, until no elements need to be swapped. The
 * bigger element will rise to top by swapping like bubble, so it names.
 * </p>
 *
 * The bubble sort algorithm designed as following:
 * <li>
 * 1. Compare the two adjacent elements as a pair, from the first pair to last
 * pair, swap the two if the first one is bigger than the second one. Then, the
 * last element must be the biggest, remove the biggest one from unordered
 * region.
 * </li>
 * <li>
 * 2. Repeat step1 on the elements in the unordered region until no element pair
 * need to be compared.
 * </li>
 *
 * The time complexity of bubble sort is O(n^2).
 *
 * <p>
 * Stability: Bubble sort is swapping bigger element backward. Comparing is
 * comparing the adjacent two elements, swapping is also in the adjacent two
 * elements. So, if the two adjacent elements equal, you will not swap them. And
 * if the two equal elements are not adjacent, even though they are adjacent by
 * swapping the front other elements, you still will not swap them. The equal
 * elements order are not changed in sorting, so bubble sort is stable.
 * </p>
 */
public class BubbleSort {

    /**
     * The bubble sort.
     * @param a The array to be sorted
     */
    public static void sort(int[] a) {
        System.out.println("In Bubble Sort:");

        // The outer loop: Limit the count of elements in each bubble sort comparison.
        for (int i = a.length - 1; i >= 1; i--) {

            // The inner loop: Comparing the elements whose subscript from 0 to i-1.
            for (int j = 0; j <= i - 1; j++) {

                // The sorting process.
                if (a[j] > a[j + 1]) {
                    int t = a[j];
                    a[j] = a[j + 1];
                    a[j + 1] = t;
                }
            }
            System.out.println(String.format("Round {0}: ", a.length - i));
            for (int e : a) {
                System.out.print(e + " ");
            }
            System.out.println();
        }
    }

}