冒泡排序

冒泡排序：

相邻数据逐个比较

复杂度：

几种写法：

        int[] arr = {5,2,1,3};
        //升序
        for (int i = 0; i < arr.length-1; i++) {
            for (int j = i; j < arr.length-1; j++) {
                if (arr[i] > arr[j+1]) {
                    int temp = arr[i];
                    arr[i] = arr[j+1];
                    arr[j+1] = temp;
                }
            }
        }
        //降序
        for (int i = 0; i < arr.length-1; i++) {
            for (int j = i; j < arr.length-1; j++) {
                if (arr[i] < arr[j+1]) {
                    int temp = arr[j+1];
                    arr[j+1] = arr[i];
                    arr[i] = temp;
                }
            }
        }