冒泡排序

package foo;

public class Main {
    public static void bubbleSort(int[] a, int len) {
        int in, out;
        for (out = len - 1; out > 0; --out) {
            for (in = 0; in < out; ++in) {
                if (a[in] > a[in+1]) {
                    swap(a, in, in + 1);
                }
            }
        }
    }
    public static void swap(int[] a, int index1, int index2) {
        int temp = a[index1];
        a[index1] = a[index2];
        a[index2] = temp;
    }
    public static void main(String[] args) {
        int[] a = new int[] {3, 2, 1, 5, 4};
        bubbleSort(a, a.length);
    }
}

冒泡排序的效率O（N*N），比较N*N/2，交换N*N/4