数据结构与算法(Java) 1：冒泡排序[含对数器]

冒泡排序不咋用了，主要拿来做教科书，辅助理解时间复杂度。时间复杂度： 

package section1;

import java.util.Arrays;

public class BubbleSort {
    public static void bubbleSort(int[] arr){
        if(arr == null || arr.length < 2) return;
        for(int end = arr.length - 1; end > 0; end--){
            for(int i = 0; i < end; i++){
                if (arr[i] > arr[i+1])
                    change(arr, i, i+1);
                System.out.println(Arrays.toString(arr));
            }
        }
    }

    public static int[] change(int[] arr, int f1, int f2){
        int flag;
        flag = arr[f1];
        arr[f1] = arr[f2];
        arr[f2] = flag;

        return arr;
    }

    public static void main(String[] args){
        int[] arr = {1, 5, 2, 9, 3, 5, 6, 2, 5};
        bubbleSort(arr);
    }
}

带对数器版：

package section1;

import java.util.Arrays;

public class BubbleSort {
    public static void bubbleSort(int[] arr){
        if(arr == null || arr.length < 2) return;
        for(int end = arr.length - 1; end > 0; end--){
            for(int i = 0; i < end; i++){
                if (arr[i] > arr[i+1])
                    change(arr, i, i+1);
//                System.out.println(Arrays.toString(arr));
            }
        }
    }

    public static int[] change(int[] arr, int f1, int f2){
        int flag;
        flag = arr[f1];
        arr[f1] = arr[f2];
        arr[f2] = flag;

        return arr;
    }

    /* test */
    public static int[] generateRandomArray(int maxSize, int maxValue){
        int[] arr = new int[(int)((maxSize + 1) * Math.random())];
        for (int i = 0; i < arr.length; i++){
            arr[i] = (int)((maxValue + 1) * Math.random()) - (int)((maxValue) * Math.random());
        }

        return arr;
    }

    /* test */
    public static boolean isEqual(int[] arr1, int[] arr2){
        if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) return false;
        if (arr1.length != arr2.length) return false;
        for(int i = 0; i < arr1.length; i++){
            if (arr1[i] != arr2[i]) return false;
        }
        return true;
    }

    /* test */
    public static int[] copyArray(int[] arr){
        int len = arr.length;
        int[] array = new int[len];
        for (int i = 0; i < len; i++) array[i] = arr[i];
        return array;
    }

    /* test */
    public static void comparator(int[] arr){
        Arrays.sort(arr);
    }

    /* test */
    public static void printArray(int[] arr){
        if (arr == null) return;
        for (int i = 0; i < arr.length; i++){
            System.out.print(arr[i] + " ");
        }
        System.out.println();
    }

    /* test */
    public static void main(String[] args){
        int maxSize = 100;
        int testTime = 500000;
        int maxValue = 100;
        boolean succeed = true;

        for (int i = 0; i < testTime; i++){
            int[] arr1 = generateRandomArray(maxSize, maxValue);
            int[] arr2 = copyArray(arr1);

            bubbleSort(arr1);
            comparator(arr2);

            if (!isEqual(arr1, arr2)){
                succeed = false;
                break;
            }
        }

        System.out.println(succeed ? "succeed!" : "False!");

        int[] arr = generateRandomArray(maxSize, maxValue);
        printArray(arr);
        bubbleSort(arr);
        printArray(arr);
    }
}