排序算法

/*
 * 排序算法
 */
class Solution {
    public void swap(int[] arr, int i, int j) {
        int temp = arr[j];
        arr[j] = arr[i];
        arr[i] = temp;
    }

    // 直接插入排序, O(n^2), 稳定
    public void directInsert(int[] arr) {
        for (int i = 0; i < arr.length; i ++) {
            for (int j = 0; j < i; j ++) {
                if (arr[j] > arr[i]) {
                    int temp = arr[i];
                    System.arraycopy(arr, j, arr, j + 1, i - j);
                    arr[j] = temp;
                }
            }
        }
    }

    // 折半插入排序，O(nlogn)，稳定
    public void binaryInsert(int[] arr) {
        for (int i = 0; i < arr.length; i ++) {
            int left = 0, right = i - 1;
            while (left <= right) {
                int mid = left + (right - left) / 2;
                if (arr[mid] < arr[i]) {
                    left = mid + 1;
                } else {
                    right = mid - 1;
                }
            }
            int temp = arr[i];
            System.arraycopy(arr, left, arr, left + 1, i - left);
            arr[left] = temp;
        }
    }

    // 选择排序， O(n^2)，不稳定
    public void directSelect(int[] arr) {
        for (int i = 0; i < arr.length - 1; i ++) {
            for (int j = i + 1; j < arr.length; j ++) {
                if (arr[i] > arr[j]) {
                    swap(arr, i, j);
                }
            }
        }
    }
    
    // 堆排序， O(nlogn)，不稳定，最大堆
    public void heap(int[] arr) {
        for (int i = arr.length - 1; i >= 0; i --) {
            for (int j = i / 2 - 1; j >= 0; j --) {
                if (j * 2 + 1 == i && i % 2 == 1) {
                    if (arr[j] < arr[j * 2 + 1]) {
                        swap(arr, j, j * 2 + 1);
                    }
                } else {
                    if (arr[j] < arr[j * 2 + 1]) {
                        swap(arr, j, j * 2 + 1);
                    }
                    if (arr[j] < arr[j * 2 + 2]) {
                        swap(arr, j, j * 2 + 2);
                    }
                }
            }
            swap(arr, 0, i);
        }
    }

    // 冒泡排序，O(n^2), 稳定
    public void bubble(int[] arr) {
        for (int i = arr.length - 1; i >= 0; i --) {
            for (int j = 0; j < i; j ++) {
                if (arr[j] > arr[j + 1]) {
                    swap(arr, j, j + 1);
                }
            }
        }
    }

    // 快排，O(nlogn)，不稳定
    public void quick(int[] arr) {
        quickSort(arr, 0, arr.length - 1);
    }
    private void quickSort(int[] arr, int left, int right) {
        if (arr == null || left >= right || arr.length <= 1) {
            return;
        }
        int mid = partition(arr, left, right);
        quickSort(arr, left, mid);
        quickSort(arr, mid + 1, right);
    }
    private int partition(int[] arr, int left, int right) {
        int temp = arr[left];
        while (left < right) {
            while (left < right && temp <= arr[right]) {
                right --;
            }
            if (left < right) {
                arr[left] = arr[right];
                left ++;
            }
            while (left < right && temp >= arr[left]) {
                left ++;
            }
            if (left < right) {
                arr[right] = arr[left];
                right --;
            }
        }
        arr[left] = temp;
        return left;
    }

    // 归并排序， O(nlogn)， 稳定
    public void mergeSort(int[] arr) {
        sort(arr, 0, arr.length - 1);
    }
    private void sort(int[] arr, int left, int right) {
        if (left < right) {
            int mid = left + (right - left) / 2;
            sort(arr, left, mid);
            sort(arr, mid + 1, right);
            merge(arr, left, mid, right);
        }
    }
    private void merge(int[] arr, int left, int mid, int right) {
        int[] temp = new int[right - left + 1];
        int i = left, j = mid + 1, index = 0;
        while (i <= mid && j <= right) {
            if (arr[i] <= arr[j]) {
                temp[index ++] = arr[i ++];
            } else {
                temp[index ++] = arr[j ++];
            }
        }
        while (i <= mid) {
            temp[index ++] = arr[i ++];
        }
        while (j <= right) {
            temp[index ++] = arr[j ++];
        }
        for (int k = 0; k < temp.length; k ++) {
            arr[left ++] = temp[k];
        }
    }
}

排序算法

原文：https://www.cnblogs.com/ipython258/p/14800379.html