Java综合整理堆排序 快速排序 归并排序

堆排序

  • 时间复杂度:0(N*log(N))
  • 空间复杂度:0(1)
  • 稳定性:不稳定
private static void heapSort(int[] arr) {
		//建堆
        crearHeap(arr);
        for (int i = 0; i < arr.length-1; i++) {
            int heapSize=arr.length-i;
            swap(arr,heapSize-1,0);
            heapSize--;
            shiftDown(arr,heapSize,0);
        }
        System.out.println(Arrays.toString(arr));
    }

    private static void crearHeap(int[] arr) {
    	// 从后往前遍历(右边非叶子节点开始), 依次进行向下调整
        for (int i = (arr.length-1-1)/2; i >=0 ; i--) {
            shiftDown(arr,arr.length,i);
        }
        
    }
	//向下调整,形成大堆
    private static void shiftDown(int[] arr, int size, int i) {
        int parent = i;
        int child = parent*2+1;
        while (child arr[child]){
                child=child+1;
            }
            if (arr[child]>arr[parent]){
                swap(arr,child,parent);
            }else {
                break;
            }
            parent=child;
            child=parent*2+1;
        }
    }
	//交换
    private static void swap(int[] arr, int child, int parent) {
        int tmp =arr[child];
        arr[child] =arr[parent];
        arr[parent]=tmp;
    }

快速排序

  • 时间复杂度:O(N^ logN) 最坏的时候O(N^2) 和基准值密切相关
  • 空间复杂度:0(logN) 最坏的时候O(N)
  • 稳定性:不稳定

递归

private static void quick(int[] arr) {
        quickSortHelper(arr,0,arr.length-1);
        System.out.println(Arrays.toString(arr));
    }

    private static void quickSortHelper(int[] arr, int left, int right) {
        if (left>=right){
            //区间只有一个元素,或者零个元素
            return;
        }
        int index = partition(arr,left,right);
        quickSortHelper(arr,left,index-1);
        quickSortHelper(arr,index+1,right);
    }

    private static int partition(int[] arr, int left, int right) {
        int i=left;
        int j=right;
        int baseValue=arr[right];
        while (i=baseValue){
                j--;
            }
            if (i 
 

非递归

public static void quickSortByLoop(int[] arr) {
        Stack stack =new Stack<>();
        stack.push(0);
        stack.push(arr.length-1);
        while (!stack.isEmpty()){
            int right = stack.pop();
            int left = stack.pop();
            if (left>=right){
                continue;
            }
            int index = partition(arr,left,right);
            //右子树
            stack.push(index+1);
            stack.push(right);
            //左子树
            stack.push(left);
            stack.push(index-1);
        }
        System.out.println(Arrays.toString(arr));
    }

    private static int partition(int[] arr, int left, int right) {
        int baseValue =arr[right];
        int i =left;
        int j =right;
        while (i=baseValue){
                j--;
            }
            if (i 
 

归并排序

  • 时间复杂度:O(NlogN)
  • 空间复杂度:O(N) 如果是链表,可以为O(1)
  • 稳定性:稳定

递归

public static void mergeSort(int[] arr){
        mergeSortHelper(arr,0,arr.length);
        System.out.println(Arrays.toString(arr));
    }

    private static void mergeSortHelper(int[] arr, int left, int right) {
        if (right-left<=1){
            return;
        }
        int mid = (right+left)/2;

        mergeSortHelper(arr,left,mid);
        mergeSortHelper(arr,mid,right);
        merge(arr,left,mid,right);
    }

    private static void merge(int[] arr, int left, int mid, int right) {
        int cur1 =left;
        int cur2 =mid;
        //两个数组合并后的结果
        int[] output=new int[right-left];
        int outputIndex=0;

        while (cur1 
 

非递归

public static void mergeSortByLoop(int[] arr){
        // gap 当前每个组中的元素个数.
        for (int gap =1;gap arr.length){
                    mid =arr.length;
                }
                if (right>arr.length){
                    right=arr.length;
                }
                merge(arr,left,mid,right);
            }
        }
        System.out.println(Arrays.toString(arr));
    }

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