九大排序算法的Java实现

1.冒泡排序

package Sort;

import java.util.Arrays;

public class BubbleSort {
    public static void main(String[] args) {
        int [] a = {1,100,234,44,3,2,4,5};
        bubbleSort(a,a.length+1);
        System.out.println(Arrays.toString(a));
    }
    public static int[] bubbleSort(int[] A, int n) {
         
        for (int i=0;i<A.length;i++){
            for (int j=i+1;j<A.length;j++){
                if (A[i] > A[j]){
                    int tmp = A[i];
                    A[i] = A[j];
                    A[j] = tmp;
                }
            }
        }
        
    return A;
    }
}

2.快速排序

package Sort;

import java.util.Arrays;

public class QuickSort {

    public static void main(String[] args) {
        int A[] = {1,6,9, 2, 3, 1, 5, 4 };
        quickSort(A, 0, 7);
        System.out.println(Arrays.toString(A));
    }

    public static void quickSort(int[] A, int left, int right) {

        if (left < right) {
            // 一次划分
            int mid = partion(A, left, right);
            quickSort(A, 0, mid - 1);
            quickSort(A, mid + 1, right);
        }
    }

    public static void swap(int[] A, int l, int r) {
        int tmp = A[l];
        A[l] = A[r];
        A[r] = tmp;

    }

    public static int partion(int[] a, int left, int right) {
        // 轴值，默认选取数组的第一个数字
        while (left < right) {
            while (left < right && a[left] <= a[right]) {
                right--;
            }
            if (left<right){
                swap(a, left, right);
            }
            while (left < right && a[left] <= a[right]) {
                left++;
            }
            if (left<right){
                swap(a, left, right);
            }
        }
        return left;
    }

}

3.插入排序

package Sort;

public class InsertionSort {
    public int[] insertionSort(int[] A, int n) {
        int i, j, temp;
          
        for(i = 1; i < n; i++){
            temp = A[i];
            for(j = i; j > 0 && A[j - 1] > temp; j-- ){
                A[j] = A[j - 1];
            }
            A[j] = temp;
        }
          
        return A;
    }
}

3.1希尔排序（插入排序的一种）

package Sort;

import java.util.Arrays;

public class ShellSort {

    public static void main(String[] args) {
        int[] a = { 54, 35, 48, 36, 27, 12, 44, 44, 8, 14, 26, 17, 28 };
        sort(a);
        System.out.println(Arrays.toString(a));
    }

    public static void sort(int[] a) {
        // 设置步长，默认为数组长度的一半
        int step = a.length / 2;
        while (step >= 1) {
            for (int i = step; i < a.length; i += step) {
                int tmp = a[i];
                int j;
                for (j = i; j > 0 && a[j - step] > tmp; j -= step) {
                    a[j] = a[j - step];//元素后移
                }
                a[j] = tmp;//插入的位置，注意此时j在for循环中已经进行了一次--
            }
            step /= 2;
        }
    }

}

4.选择排序

package Sort;

public class SelectionSort {
    public int[] selectionSort(int[] A, int n) {
        // write code here
        for (int i = 0; i < n - 1; i++) {
            int index = i;
            int j;
            // 找出最小值得元素下标
            for (j = i + 1; j < n; j++) {
                if (A[j] < A[index]) {
                    index = j;
                }
            }
            int tmp = A[index];
            A[index] = A[i];
            A[i] = tmp;
        }
        return A;
    }
}

5. 归并排序

package Sort;


public class MergeSort {

    public static void main(String[] args) {

        int[] A = { 1, 4, 3, 2, 5 };
        mergeSort(A, 5);
        for (int i = 0; i < A.length; i++) {
            System.out.println(A[i]);
            
        }
    }

    public static int[] mergeSort(int[] A, int n) {
        // write code here
        sort(A, 0, n - 1);
        return A;
    }

    public static void sort(int[] A, int left, int right) {
        if (left < right) {
            int mid = (left + right) / 2;
            sort(A, left, mid);
            sort(A, mid + 1, right);
            merge(A, left, mid, right);
        }
    }

    public static void merge(int[] A, int left, int mid, int right) {
        // 临时数组

        int n = right - left + 1;
        int[] tmpArr = new int[n];
        int l = left;
        int r = mid + 1;
        int t = 0;// 临时数组下标元素

        // 比较两子序列元素的大小
        while (l <= mid && r <= right) {
            if (A[l] < A[r]) {
                tmpArr[t++] = A[l++];
            } else {
                tmpArr[t++] = A[r++];
            }
        }

        // 剩余的加入临时数组
        while (l <= mid) {
            tmpArr[t++] = A[l++];
        }
        // 剩余的加入临时数组
        while (r <= right) {
            tmpArr[t++] = A[r++];
        }

        // 把临时数组元素放回原数组
        for (int i = 0; i < t; i++) {
            A[left + i] = tmpArr[i];
        }

    }
}

 6.堆排序

package Sort;

import java.util.Arrays;

public class HeapSort {

    public static void main(String[] args) {
        int[] a = { 2, 5, 9, 6, 1, 4, 8, 7, 12, 50 };
        sort(a);
        System.out.println(Arrays.toString(a));
    }

    public static void sort(int[] a) {
        int len = a.length;
        for (int i = 0; i < len - 1; i++) {
            // 建堆
            buildHeap(a, len - 1 - i);
            // 交换堆顶元素和最后一个元素
            swap(a, 0, len - 1 - i);
        }
    }

    private static void swap(int[] a, int i, int j) {
        // TODO Auto-generated method stub
        int tmp = a[i];
        a[i] = a[j];
        a[j] = tmp;

    }

    public static void buildHeap(int[] a, int lastIndex) {
        // 从最后一个节点的父节点开始
        for (int i = (lastIndex - 1) / 2; i >= 0; i--) {
            // 当前节点存在子节点
            while (i * 2 + 1 <= lastIndex) {
                // 左节点下标值
                int l = i * 2 + 1;
                // 右结点下标值
                int r = i * 2 + 2;

                // 默认左节点为最大值
                int biggerIndex = l;
                // 存在右结点
                if (l < lastIndex) {
                    // 右结点的值比左节点大
                    if (a[r] > a[l]) {
                        biggerIndex = r;
                    }
                }
                // 当前节点的值比孩子节点的最小值小，交换
                if (a[i] < a[biggerIndex]) {
                    swap(a, i, biggerIndex);
                    // 把最大值下标赋给当前节点，进入下一次while循环判断
                    i = biggerIndex;
                } else {
                    break;
                }

            }

        }
    }

}

7.计数排序

8.基数排序

9.桶排序