几种常用的排序

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1. 冒泡排序

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

1. 选择排序

public static void selectionSort(int[] arr) {
    int len = arr.length;
    for (int i = 0; i < len - 1; i++) {
        int minIndex = i;
        for (int j = i + 1; j < len; j++) {
            if (arr[j] < arr[minIndex]) {
                minIndex = j;
            }
        }
        if (minIndex != i) {
            int temp = arr[i];
            arr[i] = arr[minIndex];
            arr[minIndex] = temp;
        }
    }
}

1. 插入排序

public static void insertionSort(int[] arr) {
    int len = arr.length;
    for (int i = 1; i < len; i++) {
        int cur = arr[i];
        int j = i - 1;
        while (j >= 0 && arr[j] > cur) {
            arr[j+1] = arr[j];  
            j--;
        }
        arr[j+1] = cur;
    }
}

1. 快速排序

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

1. 归并排序

public static void mergeSort(int[] arr, int left, int right) {
    if (left >= right) {
        return;
    }
    int mid = left + (right - left) / 2;
    mergeSort(arr, left, mid);
    mergeSort(arr, mid + 1, right);
    merge(arr, left, mid, right);
}
private static void merge(int[] arr, int left, int mid, int right) {
    int[] temp = new int[right - left + 1];
    int i = left, j = mid + 1;
    int k = 0;
    while (i <= mid && j <= right) {
        if (arr[i] <= arr[j]) {
            temp[k++] = arr[i++];
        } else {
            temp[k++] = arr[j++];
        }
    }
    while (i <= mid) {
        temp[k++] = arr[i++];
    }
    while (j <= right) {
        temp[k++] = arr[j++];
    }
    for (int p = 0; p < temp.length; p++) {
        arr[left + p] = temp[p];
    }
}

这些排序算法的时间复杂度从O(n^2)到O(nlogn)不等，其中冒泡排序和选择排序为O(n^2)，插入排序和归并排序为O(nlogn)，快速排序的时间复杂度为O(nlogn)。