java 树形选择排序_选择排序、树形排序、堆排序的java代码实现

选择排序Java代码实现：

public static void selectionSort(int[] arr) {
    int n = arr.length;

    // One by one move boundary of unsorted subarray
    for (int i = 0; i < n-1; i++) {
        // Find the minimum element in unsorted array
        int min_idx = i;
        for (int j = i+1; j < n; j++)
            if (arr[j] < arr[min_idx])
                min_idx = j;

        // Swap the found minimum element with the first element
        int temp = arr[min_idx];
        arr[min_idx] = arr[i];
        arr[i] = temp;
    }
}

树形排序Java代码实现：

public static void treeSort(int[] arr) {
    TreeSet<Integer> tree = new TreeSet<>();
    for (int i = 0; i < arr.length; i++) {
        tree.add(arr[i]);
    }

    int index = 0;
    for (Integer i : tree) {
        arr[index++] = i;
    }
}

堆排序Java代码实现：

public static void heapSort(int[] arr) {
    int n = arr.length;

    // Build heap (rearrange array)
    for (int i = n / 2 - 1; i >= 0; i--)
        heapify(arr, n, i);

    // One by one extract an element from heap
    for (int i=n-1; i>=0; i--)
    {
        // Move current root to end
        int temp = arr[0];
        arr[0] = arr[i];
        arr[i] = temp;

        // call max heapify on the reduced heap
        heapify(arr, i, 0);
    }
}

// To heapify a subtree rooted with node i which is
// an index in arr[]. n is size of heap
static void heapify(int arr[], int n, int i)
{
    int largest = i; // Initialize largest as root
    int l = 2*i + 1; // left = 2*i + 1
    int r = 2*i + 2; // right = 2*i + 2

    // If left child is larger than root
    if (l < n && arr[l] > arr[largest])
        largest = l;

    // If right child is larger than largest so far
    if (r < n && arr[r] > arr[largest])
        largest = r;

    // If largest is not root
    if (largest != i)
    {
        int swap = arr[i];
        arr[i] = arr[largest];
        arr[largest] = swap;

        // Recursively heapify the affected sub-tree
        heapify(arr, n, largest);
    }
}