算法-快排

体会轴的概念

 先做一个方法,定义一个数组,以最后一个数为轴,把比轴小的数放在轴的左边,比轴大的数放在轴的右边

public static void LastAxleSort(int[]arr,int leftB,int rightB)
        {
            

            int left = leftB;
            int last = rightB;
            int right = rightB-1;


            while (left <right)
            {
                while (arr[left] <= arr[last] && left < right)
                {
                    left++;
                }

                while (arr[right] >= arr[last] && left < right)
                {
                    right--;
                }

                if (left < right)
                {
                    ExchangeLocation(arr, left, right);
                }
                else if (left==right)
                {
                    break;
                }

            }

            if (left<last&& arr[left]>arr[last])
            {
                ExchangeLocation(arr, left, last);
            }

        }

扩展为取数组的一部分

public static int LastAxleSortPart1(int[] arr, int leftB, int rightB)
        {
            

            int left = leftB;
            int last = rightB;
            int right = rightB - 1;

            int lastValue = arr[last];


            while (left < right)
            {
                while (arr[left] <= arr[last] && left <= right)
                {
                    left++;
                }

                while (arr[right] >= arr[last] && left < right)
                {
                    right--;
                }

                if (left < right)
                {
                    ExchangeLocation(arr, left, right);
                }
               

            }

            if (left < last&& arr[left]>arr[last])
            {
                ExchangeLocation(arr, left, last);
            }
            //Console.WriteLine();
            //Console.WriteLine($"左边界:{leftB},右边界:{rightB},排序轴值:{lastValue},返回轴:{left}");
            //PrintArr(arr);
            return left;

        }

递归调用的方法

public static void QuickSortPart(int[] arr,int leftB,int rightB)
        {
            if (leftB>=rightB)
            {
                return;
            }
            int axle = LastAxleSortPart1(arr, leftB, rightB);


            QuickSortPart(arr, leftB, axle-1);
            QuickSortPart(arr, axle+1, rightB);

            //Console.WriteLine($"**");

        }