文章标题

public class Sort {    public static void swap(int[] array,int i,int j){        int temp = array[i];        array[i] = array[j];        array[j] = temp;    }    public static  void insertSort(int[] arrayToSort){        for( int i = 0 ; i < arrayToSort.length; ++i){            //从i的位置往前去排 保证i前面的分片是有序的            for( int j = i-1 ; j >= 0 ; --j){                if( arrayToSort[j+1] < arrayToSort[j]){                    swap(arrayToSort, j+1,j);                }            }        }    }    //选择排序    public static  void selectSort(int[] arrayToSort){        //每次选择arrayToSort[i] 后面最小的元素来进行交换        for( int i = 0 ; i < arrayToSort.length ; ++i){            int min = i;            for( int j = i+1; j < arrayToSort.length ; ++j){                if( arrayToSort[j] < arrayToSort[min]){                    min = j;                }            }            swap(arrayToSort,min,i);        }    }    //归并排序 时间复杂度O(nlogn) 空间复杂度 O(n)+O(logn)    //可以将数组分成二组。依次类推，当分出来的小组只有一个数据时，可以认为这个小组组内已经达到了有序，    // 然后再合并相邻的二个小组就可以了。这样通过先递归的分解数列，再合并数列就完成了归并排序    public static void mergerSort(int[] arrayToSort){        sort(arrayToSort,0,arrayToSort.length-1);    }    private  static void sort(int[] array ,int left,int  right) {        if (left < right) {            int center = (left + right) / 2;            //对左边递归            sort(array, left, center);            //对右边递归            sort(array, center + 1, right);            //mergerArray            mergerArray(array, left, center, right);        }    }    private static void mergerArray(int array[],int left,int mid,int right){       int[] tmp = new int[array.length];       int r1 = mid + 1;       int tIndex = left;       //tmp 数组索引       int sIndex = left;       //swap 时的索引       while (left <= mid && r1 <= right){           if(array[left] <= array[r1]){               tmp[tIndex++] = array[left++];           }else {               tmp[tIndex++] = array[r1++];           }       }       while (left <= mid){           tmp[tIndex++] = array[left++];       }       while (r1 <= right){           tmp[tIndex++] = array[r1++];       }       while (sIndex <= right){           array[sIndex] = tmp[sIndex++];       }    }    //快速排序的每一轮就是将这一轮的基准数归位，直到所有的数都归为为止，排序结束。（类似冒泡）. partition是返回一个基准值的index, index 左边都小于该index的数，右边都大于该index的数。    public static void quickSort(int[] arrayToSort,int left ,int right){        int p ;        if( left < right){            p = parition(arrayToSort,left,right);            quickSort(arrayToSort,left,p-1); // 从[left,p-1]            quickSort(arrayToSort, p + 1,right);//从[p+1,right]        }    }    //三个指针 一个 是 i  从left开始 j 是从right开始 还有个基准变量    private static int parition(int[] array,int left,int right){        int povit = left;        int j = right;        int i = left;        int povitNum = array[povit];        while (i != j){            while (array[j] >= povitNum && i != j){                j--;            }            while ( array[i] <= povitNum && i != j){                i++;            }            if(i == j){                swap(array,povit,i);            }            swap(array,i,j);        }        return i;    }    public static int[] getMinKNumsByHeap(int[] arr,int k){        if(arr == null || k <= 0){            return null;        }        /*int[] heap = new int[k];        for(int i = 0  ; i < k; i++){            heapInsert(heap,arr[i],i);        }        for(int i = k ; i < arr.length;i++){            if(arr[i] < heap[0]){                heap[0] = arr[i];                heapify(heap,0,k);            }        }        return heap;*/        int[] heap = creatHeap(arr,k);        for(int i = k ; i < arr.length ; ++i){            if(arr[i] > heap[0]){                insert(heap,arr[i]);            }        }        return  heap;    }    private static void heapInsert(int[] arr, int value, int index) {        arr[index] = value;        while (index != 0){            int parent = (index-1)/2;            if(arr[parent] <arr[index]){                swap(arr,index,parent);                index = parent;            }else {                break;            }        }    }    public static void heapify(int[] arr,int index,int heapsize){        int left = index * 2 + 1;        int right = index * 2 +2 ;        int largest = index;        while (left < heapsize){            if(arr[left] > arr[index]){                largest = left;            }            if(right < heapsize && arr[right] > arr[largest]){                largest = right;            }            if(largest != index){                swap(arr,largest,index);            }else {                break;            }            index = largest;            left = index * 2 + 1;            right = index * 2 + 2;        }    }    public static int[] creatHeap(int[] a,int k){        int[] result = new int[k];        for(int i = 0 ;i < k; ++i){            result[i] = a[i];        }        for(int i = 0 ; i < k; ++i){            int child = i;            int parent = (i -1)/2;            int temp = a[i];            while(parent >= 0 && child != 0 && result[parent] > temp){                result[child] = result[parent];                child = parent;                parent = (parent -1)/2;            }            result[child] = temp;        }        return result;    }    public static void insert(int[] a,int value){        a[0] = value;        int parent = 0;        while (parent < a.length){            int lchild = parent*2 + 1;            int rchild = parent*2 + 2;            int minIndex = parent;            if(lchild < a.length && a[parent] > a[lchild]){                minIndex = lchild;            }            if(rchild < a.length && a[minIndex] > a[rchild]){                minIndex = rchild;            }            if(minIndex == parent){                return ;            }else {                swap(a,parent,minIndex);                parent = minIndex;            }        }    }    public static void main(String[] args) {//        int[] array = {2,1,49,30,32,-1,20,50,49};        int[] array = {26,5,98,108,28,99,100};/*        Scanner in = new Scanner(System.in);        int m = in.nextInt();        array = new int[m];        for(int i = 0 ; i < m;i++){            array[i] = in.nextInt();        }*/        System.out.println("before sort:" + Arrays.toString(array));        long start = System.nanoTime();//        insertSort(array);//      selectSort(array);//        mergerSort(array);//        quickSort(array,0,array.length - 1);        int[] heap = getMinKNumsByHeap(array,3);        System.out.println(System.nanoTime() - start);        System.out.println("After sort:"+Arrays.toString(heap));    }}