摘要：冒泡排序插入排序選擇排序堆排序父節點索引尾節點索引歸并排序快速排序附錄交換方法基于策略模式的主程序實現定義一個數組構造函數初始化數組遍歷數組中每一個元素展示

「博客搬家」  原地址: 簡書  原發表時間: 2017-08-17

網上有很多排序算法的總結，不過有很多缺點，比如有些根本就是錯的，無法通過測試用例，有些過于冗長。所以我總結了一套短小精悍的 Java 實現，經測試，該套實現可通過牛客網的關于此的所有測試用例。

public class BubbleSort implements KySort {
    public void kySort(int[] a, int size) {
        for (int i = 0; i < size - 1; i++) {
            for (int j = 0; j < size - i - 1; j++) {
                if (a[j] > a[j + 1]) {
                    swap(a, j, j + 1);
                }
            }
        }
    }
}

public class InsertSort implements KySort {
    public void kySort(int[] a, int size) {
        for (int i = 1; i < size; i++) {
            int temp = a[i];
            int j = i;
            while (j > 0 && a[j - 1] > temp) {
                a[j] = a[j - 1];
                j--;
            }
            a[j] = temp;
        }
    }
}

public class SelectSort implements KySort {
    public void kySort(int[] a, int size) {
        for (int i = 0; i < size - 1; i++) {
            int min = i;
            for (int j = i + 1; j < size; j++) {
                if (a[j] < a[min]) {
                    min = j;
                }
            }
            if (i != min) {
                swap(a, i, min);
            }
        }
    }
}

public class HeapSort implements KySort {
    public void kySort(int[] a, int n) {
        for (int i = n / 2; i >= 0; i--) {
            heapAdjust(a, i, n - 1);
        }
        for (int i = n - 1; i > 0; i--) {
            swap(a, 0, i);
            heapAdjust(a, 0, i - 1);
        }
    }

    /**
     * @param index 父節點索引
     * @param n     尾節點索引
     */
    private void heapAdjust(int[] a, int index, int n) {
        int temp = a[index];
        for (int child = index * 2 + 1; child <= n; child = index * 2 + 1) {
            if (child < n && a[child] < a[child + 1]) {
                child++;
            }
            if (temp > a[child]) break;
            a[index] = a[child];
            index = child;
        }
        a[index] = temp;
    }
}

public class MergeSort implements KySort {
    public void kySort(int[] a, int size) {
        sort(a, 0, size - 1, new int[a.length]);
    }

    private void sort(int[] a, int left, int right, int[] temp) {
        if (left >= right) return;
        int mid = (left + right) / 2;
        sort(a, left, mid, temp);
        sort(a, mid + 1, right, temp);
        merge(a, left, mid, right, temp);
    }

    private void merge(int[] a, int left, int mid, int right, int[] temp) {
        int k = left;
        int i = left;
        int j = mid + 1;

        while (i <= mid && j <= right) {
            if (a[i] < a[j]) {
                temp[k++] = a[i++];
            } else {
                temp[k++] = a[j++];
            }
        }
        while (i <= mid) {
            temp[k++] = a[i++];
        }
        while (j <= right) {
            temp[k++] = a[j++];
        }

        while (left <= right) {
            a[left] = temp[left];
            left++;
        }
    }
}

public class QuickSort implements KySort {
    @Override
    public void kySort(int[] a, int size) {
        quickSort(a, 0, size - 1);
    }

    private void quickSort(int[] a, int left, int right) {
        if (right - left < 2) {
            if (a[left] > a[right])
                swap(a, left, right);
            return;
        }
        int p = middleBy3(a, left, right);

        quickSort(a, left, p - 1);
        quickSort(a, p + 1, right);
    }

    private int middleBy3(int[] a, int left, int right) {
        int p = (left + right) / 2;
        int end = right;

        if (a[left] > a[p]) swap(a, left, p);
        if (a[left] > a[right]) swap(a, left, right);
        if (a[p] > a[right]) swap(a, p, right);

        int temp = a[p];
        swap(a, p, right);

        while (true) {
            while (a[++left] < temp) ;
            while (a[--right] > temp) ;
            if (left >= right) break;
            else swap(a, left, right);
        }
        swap(a, left, end);
        return left;
    }
}

public class Util {
    public static void swap(int[] a, int i, int j) {
        int k = a[i];
        a[i] = a[j];
        a[j] = k;
    }
}

public class SortMain {
    private static KySort sorter;
    private int[] a;//定義一個數組

    private SortMain(int... values) {   //構造函數
        a = values;
    }

    public static void main(String[] args) {
        setSorter(new QuickSort());
        SortMain arr;
        arr = new SortMain(5, 4, 3, 2, 1, 0);
        arr.display();
        arr.kySort();
        arr.display();
        System.out.println("--------");
        arr = new SortMain(54, 35, 48, 36, 27, 12, 44, 44, 8, 14, 26, 17, 28);
        arr.display();
        arr.kySort();
        arr.display();
        System.out.println("--------");
        arr = new SortMain(32, 103, 24, 88, 95, 70, 97, 15, 102, 6, 79, 46, 51, 37, 93, 108, 9, 58, 53, 58, 79, 36, 58, 91, 78, 58, 61, 81);    //初始化數組
        arr.display();
        arr.kySort();
        arr.display();
    }

    private static void setSorter(KySort sorter) {
        SortMain.sorter = sorter;
    }

    private void display() {
        for (int i : a) {   //遍歷數組中每一個元素
            System.out.print(i + " ");   //展示
        }
        System.out.println();
    }

    private void kySort() {
        sorter.kySort(a, a.length);
    }
}