1. 排序

1. 快速排序

public static void qSort(int[] arr, int left, int right){
    if (left >= right) return;

    int i = left - 1, j = right + 1;
    int key = arr[left];
    while (i < j){
        while (arr[++i] < key);
        while (arr[--j] > key);
        if (i < j){
            int t = arr[i];
            arr[i] = arr[j];
            arr[j] = t;
        }
    }
    qSort(arr, left, j);
    qSort(arr, j + 1, right);
}

2. 归并排序

public static void merge(int[] nums, int left, int mid, int right, int[] temp){
        for (int i = left; i <= right; i++) temp[i] = nums[i];
        int i = left, j = mid + 1;
        for (int k = left; k <= right; k++){
            if (i > mid){
                nums[k] = temp[j];
                j++;
            }
            else if (j > right){
                nums[k] = temp[i];
                i++;
            }
            else if (temp[i] < temp[j]){
                nums[k] = temp[i];
                i++;
            }
            else{
                nums[k] = temp[j];
                j++;
            }
        }
    }

    public static void mergeSort(int[] nums, int left, int right, int[] temp){
        if (left >= right) return;
        int mid = left + (right - left) / 2;
        mergeSort(nums, left, mid, temp);
        mergeSort(nums, mid + 1, right, temp);
        if (nums[mid] <= nums[mid + 1]) return;
        merge(nums, left, mid, right, temp);
    }