基本排序算法

leetcode: 排序算法

冒泡排序

• 基础版排序：

public class BubbleSort {
    public void sort(int[] arr) {
        for (int i = 0; i < arr.length - 1; i++) {
            for (int j = 0; j < arr.length - 1 - i; j++) {
                if (arr[j] > arr[j + 1]) {
                    int temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                }
            }
        }
    }
}

• 优化版排序：

public class BubbleSort {
    public void sort(int[] arr) {
        for (int i = 0; i < arr.length - 1; i++) {
            boolean flag = true;
            for (int j = 0; j < arr.length - 1 - i; j++) {
                if (arr[j] > arr[j + 1]) {
                    int temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                    flag = false;
                }
            }
            if (flag) break;
        }
    }
}

快速排序

public class QuickSort {
    public void sort(int[] arr) {
        quickSort(arr, 0, arr.length - 1);
    }

    public void quickSort(int[] arr, int begin, int end) {
        if (begin >= end) return;
        int pivot = arr[begin];
        int left = begin;
        int right = end;
        while (left < right) {
            while (left < right && arr[right] >= pivot) right--;
            arr[left] = arr[right];
            while (left < right && arr[left] <= pivot) left++;
            arr[right] = arr[left];
        }
        arr[left] = pivot;
        quickSort(arr, begin, left - 1);
        quickSort(arr, left + 1, end);
    }
}

选择排序

public class SimpleSelectSort {
    public void sort(int[] arr) {
        for (int i = 0; i < arr.length - 1; i++) {
            int maxIndex = 0;
            for (int j = 0; j < arr.length - i; j++) {
                if (arr[j] > arr[maxIndex]) maxIndex = j;
            }
            int temp = arr[maxIndex];
            arr[maxIndex] = arr[arr.length - 1 - i];
            arr[arr.length - 1 - i] = temp;
        }
    }
}

插入排序

归并排序

public class MergeSort {
    public void sort(int[] arr) {
        mergeSort(arr, 0, arr.length - 1);
    }

    private void mergeSort(int[] arr, int begin, int end) {
        if (begin >= end) return;
        int middle = (begin + end) >> 1;
        mergeSort(arr, begin, middle);
        mergeSort(arr, middle + 1, end);
        merge(arr, begin, middle, end);
    }

    private void merge(int[] arr, int begin, int mid, int end) {
        int[] temp = new int[end - begin + 1];
        int i = begin;
        int j = mid + 1;
        int index = 0;
        while (i <= mid && j <= end) {
            if (arr[i] <= arr[j])
                temp[index++] = arr[i++];
            else
                temp[index++] = arr[j++];
        }
        while (i <= mid) temp[index++] = arr[i++];
        while (j <= end) temp[index++] = arr[j++];
        for (int num : temp) arr[begin++] = num;
    }
}

public class MergeSort {
    public void sort(int[] arr) {
        mergeSort(arr, 0, arr.length - 1);
    }

    private void mergeSort(int[] arr, int begin, int end) {
        if (begin >= end) return;
        int middle = (begin + end) >> 1;
        mergeSort(arr, begin, middle);
        mergeSort(arr, middle + 1, end);
        merge(arr, begin, middle, end);
    }

    private void merge(int[] arr, int begin, int mid, int end) {
        int[] temp = new int[end - begin + 1];
        int i = begin;
        int j = mid + 1;
        int index = 0;
        while (i <= mid || j <= end) {
            if (i > mid) temp[index++] = arr[j++];
            else if (j > end) temp[index++] = arr[i++];
            else if (arr[i] <= arr[j]) temp[index++] = arr[i++];
            else temp[index++] = arr[j++];
        }
        for (int num : temp) arr[begin++] = num;
    }
}