Java 实现常见排序算法

Java 实现常见排序算法

1. 综述

　　复习常见排序算法，用Java实现。

2. 代码

package cn.edu.tju.scs;

public class Sort {
    public static void main(String [] args){
        
        int[] intArray = {3, 5, 1, 4, 7, 9, 8, 2, 6};
        System.out.print("排序前：");print(intArray);
        long beginTime = System.nanoTime();
        
//        bubbleSort(intArray);
//        selectSort(intArray);
//        insertionSort(intArray);
//        mergeSort(intArray);
//        quickSort(intArray);
//        heapSort(intArray);

        long endTime = System.nanoTime();    
        System.out.print("排序后：");print(intArray); 
        System.out.println("用时：" + (endTime - beginTime) + "ns");
    }

    private static void heapSort(int[] intArray) {
        // build Max Heap
        for (int i = intArray.length - 1; i >= 0; i--)
            maxHeapify(intArray, intArray.length - 1, i);
        
        for (int i = intArray.length - 1; i > 0; i--) {
            swap(intArray, 0, i);
            maxHeapify(intArray, i - 1, 0);
        }
    }

    private static void maxHeapify(int[] intArray, int lastNode, int rootNode) {
        int lchild = 2 * rootNode + 1;
        int rchild = lchild + 1;

        // has two children
        while (lchild < lastNode) {
            if (intArray[rootNode] >= intArray[lchild] && intArray[rootNode] >= intArray[rchild])
                return;
            
            if (intArray[lchild] >= intArray[rchild]) {
                swap(intArray, lchild, rootNode);
                rootNode = lchild;
            } else {
                swap(intArray, rchild, rootNode);
                rootNode = rchild;
            }
            lchild = 2 * rootNode + 1;
            rchild = lchild + 1;
        }
        // has only left child
        if (lchild == lastNode) {
            if (intArray[rootNode] < intArray[lchild])
                swap(intArray, lchild, rootNode);
        }
    }

    private static void quickSort(int[] intArray) {
        quickSort(intArray, 0, intArray.length - 1);
    }

    private static void quickSort(int[] intArray, int begin, int end) {
        if (end - begin < 1) return;
        if (end - begin < 2){
            if (intArray[end] < intArray[begin])
                swap(intArray, begin, end);
            return;
        }
        // partition begin
        int left = begin;
        int right = end;
        int x = intArray[left];
        while (left < right) {
            while (intArray[right] >= x && left < right) 
                right--;
            if (left < right){
                intArray[left] = intArray[right];
                left++;
            }
            
            while (intArray[left] < x && left < right) 
                left++;
            if (left < right){
                intArray[right] = intArray[left];
                right--;
            }
        }
        intArray[right] = x;
        // partition end
        quickSort(intArray, begin, right - 1);
        quickSort(intArray, right + 1, end);
    }

    private static void mergeSort(int[] intArray) {
        mergeSort(intArray, 0, intArray.length - 1);
    }

    private static void mergeSort(int[] intArray, int begin, int end) {
        if (end - begin < 2){
            // sort 2 number
            if (intArray[begin] > intArray[end])
                swap(intArray, begin, end);
        } else {
            int mid = (begin + end) / 2;
            mergeSort(intArray, begin, mid);
            mergeSort(intArray, mid + 1, end);
            merge(intArray, begin, mid, end);
        }
    }

    private static void merge(int[] intArray, int begin, int mid, int end) {
        int [] tmpArray = new int[end - begin + 1];
        int iter1 = begin;
        int iter2 = mid + 1;
        int i = 0;
        while (iter1 <= mid && iter2 <= end) {
            if (intArray[iter2] < intArray[iter1]) {
                tmpArray[i] = intArray[iter2];
                iter2++;
                i++;
            } else {
                tmpArray[i] = intArray[iter1];
                iter1 ++;
                i++;
            }                
        }
        if (iter1 > mid){
            for (int j = iter2; j <= end; j++) {
                tmpArray[i++] = intArray[j];
            }
        }
        if (iter2 > end){
            for (int j = iter1; j <= mid; j++){
                tmpArray[i++] = intArray[j];
            }
        }
        for (i = 0; i < tmpArray.length; i++)
            intArray[begin + i] = tmpArray[i];
    }

    private static void insertionSort(int[] intArray) {
        
        for (int i = 1; i < intArray.length; i++) {
            int flag = i;
            if (intArray[flag] >= intArray[flag - 1])
                continue;
            int temp = intArray[flag]; // temp need to inserted into the sequence
            if (intArray[flag] < intArray[0]) {
                // move all items one back
                for (int j = flag; j > 0; j--) {
                    intArray[j] = intArray[j - 1];
                }
                intArray[0] = temp;
            } else {    // need insertion
                int left = 0, right = flag - 1, mid = 0;
                while (right - left != 1) {
                    mid = (right + left) / 2;
                    if (intArray[mid] <= temp)
                        left = mid;
                    else 
                        right = mid;                        
                }
                for (int j = flag; j > right; j--){
                    intArray[j] = intArray[j - 1];
                }
                intArray[right] = temp;
            }
        }
    }

    private static void selectSort(int[] intArray) {
        int tmp = 0;
        for (int i = 0; i < intArray.length; i++) {
            tmp = intArray[i];
            for (int j = i + 1; j < intArray.length; j++)
                if (tmp > intArray[j]) {
                    int temp = tmp;
                    tmp = intArray[j];
                    intArray[j] = temp;
                }
            intArray[i] = tmp;
        }        
    }

    private static void print(int[] intArray) {
        for(int i : intArray) {
            System.out.print(i + " ");
        }
        System.out.println();
    }

    private static void bubbleSort(int[] intArray) {
        for(int i = 0; i < intArray.length; i++)
            for(int j = 0; j < intArray.length - 1 - i; j++)
                if(intArray[j] > intArray[j + 1])
                    swap(intArray, j, j + 1);
    }

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