Java 8大排序算法

直接插入排序

//直接插入排序
    public int[] insertSort(int[] a) {
        for (int i = 1; i < a.length; i++) {
            int j = i - 1;
            for (; j >= 0 && a[j] > a[i]; j--) {
                a[j + 1] = a[j];//往后移
            }
            a[j + 1] = a[i];
        }
        return a;
    }

希尔排序

//希尔排序
    public int[] shellSort(int[] a) {
        int n = a.length;
        int gap = n;//数组数
        while (gap > 0) {
            gap = gap / 2;//将数组缩小一半
            for (int x = 0; x < gap; x++) {//将每组数进行直接插入排序

                //直接插入排序
                for (int i = x + gap; i < n; i += gap) {
                    int j = i - gap;
                    for (; j >= 0 && a[j] > a[i]; j -= gap) {
                        a[j + gap] = a[j];
                    }
                    a[j + gap] = a[i];
                }
            }
        }
        return a;
    }

简单选择排序

//简单选择排序
    public int[] simpleSort(int[] a) {
        int n = a.length;
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j <= n; j++) {
                if (a[j] < a[i]) {
                    int temp = a[i];
                    a[i] = a[j];
                    a[j] = temp;
                }
            }
        }
        return a;
    }

堆排序

//堆排序
    public void heapSort(int[] a) {
        System.out.println("开始排序");
        int arrayLength = a.length;
        //循环建堆，每次把最大值放在最后，不参与下一次的建堆
        for (int i = 0; i < arrayLength - 1; i++) {
            //建堆
            buildMaxHeap(a, arrayLength - 1 - i);
            //交换堆顶和最后一个元素
            swap(a, 0, arrayLength - 1 - i);
            System.out.println(Arrays.toString(a));
        }
    }


    private void swap(int[] data, int i, int j) {
        int tmp = data[i];
        data[i] = data[j];
        data[j] = tmp;
    }

    //对data数组从0到lastIndex建大顶堆
    private void buildMaxHeap(int[] data, int lastIndex) {
        //从lastIndex处节点（最后一个节点）的父节点开始，(lastIndex - 1) / 2为节点数
        for (int i = (lastIndex - 1) / 2; i >= 0; i--) {
            //k保存正在判断的节点
            int k = i;
            //如果当前k节点的子节点存在，把堆中最大的数放在对顶
            while (k * 2 + 1 <= lastIndex) {
                //k节点的左子节点的索引
                int biggerIndex = 2 * k + 1;
                //如果biggerIndex小于lastIndex，即biggerIndex+1代表的k节点的右子节点存在
                if (biggerIndex < lastIndex) {
                    //若果右子节点的值较大
                    if (data[biggerIndex] < data[biggerIndex + 1]) {
                        //biggerIndex总是记录较大子节点的索引
                        biggerIndex++;
                    }
                }

                //如果k节点的值小于其较大的子节点的值
                if (data[k] < data[biggerIndex]) {
                    //交换他们
                    swap(data, k, biggerIndex);
                    //将biggerIndex赋予k，开始while循环的下一次循环，重新保证k节点的值大于其左右子节点的值
                    k = biggerIndex;
                } else {
                    break;
                }
            }
        }
    }

冒泡排序

//冒泡排序
    public int[] bubbleSort(int[] a) {
        int temp = 0;
        for (int i = 0; i < a.length - 1; i++) {
            for (int j = 0; j < a.length - 1 - i; j++) {
                if (a[j] > a[j + 1]) {
                    temp = a[j];
                    a[j] = a[j + 1];
                    a[j + 1] = temp;
                }
            }
        }
        return a;
    }

快速排序

//快速排序
    public void quickSort() {
        quick(a);
        for (int i = 0; i < a.length; i++) {
            System.out.println(a[i]);
        }
    }

    public int getMiddle(int[] list, int low, int high) {
        int tmp = list[low];    //数组的第一个作为中轴
        while (low < high) {
            while (low < high && list[high] >= tmp) {
                high--;
            }

            list[low] = list[high];   //比中轴小的记录移到低端
            while (low < high && list[low] <= tmp) {
                low++;
            }

            list[high] = list[low];   //比中轴大的记录移到高端
        }
        list[low] = tmp;              //中轴记录到尾
        return low;                   //返回中轴的位置
    }

    public void _quickSort(int[] list, int low, int high) {
        if (low < high) {
            int middle = getMiddle(list, low, high);  //将list数组进行一分为二
            _quickSort(list, low, middle - 1);       //对低字表进行递归排序
            _quickSort(list, middle + 1, high);       //对高字表进行递归排序
        }
    }

    public void quick(int[] a2) {
        if (a2.length > 0) {    //查看数组是否为空
            _quickSort(a2, 0, a2.length - 1);
        }
    }

归并排序

//归并排序
    public void mergeSort(int[] arr) {
        int[] temp = new int[arr.length];
        internalMergeSort(arr, temp, 0, arr.length - 1);
    }

    private void internalMergeSort(int[] a, int[] b, int left, int right) {
        //当left==right的时，已经不需要再划分了
        if (left < right) {
            int middle = (left + right) / 2;
            internalMergeSort(a, b, left, middle);//左子数组
            internalMergeSort(a, b, middle + 1, right);//右子数组
            mergeSortedArray(a, b, left, middle, right);//合并两个子数组
        }
    }

    // 合并两个有序子序列 arr[left, ..., middle] 和 arr[middle+1, ..., right]，temp是辅助数组。
    private void mergeSortedArray(int arr[], int temp[], int left, int middle, int right) {
        int i = left;
        int j = middle + 1;
        int k = 0;

        //从两个数组中取出最小的放入临时数组
        while (i <= middle && j <= right) {
            if (arr[i] <= arr[j]) {
                temp[k++] = arr[i++];
            } else {
                temp[k++] = arr[j++];
            }
        }

        //将左数组剩下的数据复制到临时数组
        while (i <= middle) {
            temp[k++] = arr[i++];
        }
        //将右数组剩下的数据复制到临时数组
        while (j <= right) {
            temp[k++] = arr[j++];
        }
        //把数据复制回原数组
        for (i = 0; i < k; ++i) {
            arr[left + i] = temp[i];
        }
    }

基数排序

//基数排序
    public void  radixSort() {
        sort(a);
        for (int i = 0; i < a.length; i++) {
            System.out.println(a[i]);
        }
    }

    public void sort(int[] array) {
        //首先确定排序的趟数;
        int max = array[0];
        for (int i = 1; i < array.length; i++) {
            if (array[i] > max) {
                max = array[i];
            }
        }
        int time = 0;
        //判断位数;
        while (max > 0) {
            max /= 10;
            time++;
        }

        //建立10个队列;
        List<ArrayList> queue = new ArrayList<ArrayList>();
        for (int i = 0; i < 10; i++) {
            ArrayList<Integer> queue1 = new ArrayList<Integer>();
            queue.add(queue1);
        }

        //进行time次分配和收集;
        for (int i = 0; i < time; i++) {
            //分配数组元素;
            for (int j = 0; j < array.length; j++) {
                //得到数字的第time+1位数;
                int x = array[j] % (int) Math.pow(10, i + 1) / (int) Math.pow(10, i);
                ArrayList<Integer> queue2 = queue.get(x);
                queue2.add(array[j]);
                queue.set(x, queue2);
            }
            int count = 0;//元素计数器;
            //收集队列元素;
            for (int k = 0; k < 10; k++) {
                while (queue.get(k).size() > 0) {
                    ArrayList<Integer> queue3 = queue.get(k);
                    array[count] = queue3.get(0);
                    queue3.remove(0);
                    count++;
                }
            }
        }

    }