排序

/*插入排序(insert Sort)   O(n^2)*/
        public List<int> InsertSort(int[] arr)
        {
            List<int> tempArr = new List<int>();
            tempArr.Add(arr[0]);
            bool flag = false;
            for (int i = 1; i < arr.Length; i++)
            {
                for (int j = 0; j < tempArr.Count; j++)
                {
                    if (arr[i] < tempArr[j])
                    {
                        tempArr.Insert(j, arr[i]);
                        flag = true;
                        break;
                    }
                }
                if (!flag)
                {
                    tempArr.Add(arr[i]);
                }
                flag = false;
            }
            return tempArr;
        }

/*归并排序(merge Sort)  O(nlog2(n))  非递归*/
        public List<int> MergeSort(int[] arr) 
        {
            List<int> tempArr = new List<int>();//保存最后得到的数组
            int twoDouble = 2;//保存2的幂次方
            List<int> preArr = new List<int>();//保存前一个数组
            for(int i=0;i<arr.Length;i++){
                preArr.Add(arr[i]);
            }
            while (arr.Length > twoDouble/2)//当数组的长度小于2的幂次方的长度时，终止
            {
                List<int> subArr = new List<int>();//拿到合并后的数组
                tempArr.Clear();
                if (arr.Length / twoDouble > 0)//不是最后一组
                {
                    for (int i = 0; i < arr.Length / twoDouble; i++)
                    {//一定可以有2个或以上的组,而且是可以平分的
                        List<int> leftArr = new List<int>();
                        List<int> rightArr = new List<int>();
                        for (int j = i * twoDouble; j < (i * twoDouble + twoDouble / 2); j++)
                        {
                            leftArr.Add(preArr[j]);
                        }
                        for (int j = (i * twoDouble + twoDouble / 2); j < (i * twoDouble + twoDouble); j++)
                        {
                            rightArr.Add(preArr[j]);
                        }
                        subArr = MergeSortSubProgram(leftArr, rightArr);
                        for (int j = 0; j < subArr.Count; j++) //将拿到的合并后的数组添加到preArr
                        {
                            tempArr.Add(subArr[j]);
                        }
                        subArr.Clear();
                    }
                    if ((arr.Length - (arr.Length / twoDouble) * twoDouble) <= twoDouble / 2)//如果最后的数不能分为2组
                    {
                        for (int i = (arr.Length / twoDouble) * twoDouble; i < arr.Length; i++)
                        {
                            tempArr.Add(preArr[i]);
                        }
                    }
                    else {
                        List<int> leftArr = new List<int>();
                        List<int> rightArr = new List<int>();
                        for (int i = (arr.Length / twoDouble) * twoDouble; i < (arr.Length / twoDouble) * twoDouble+twoDouble / 2; i++)
                        {
                            leftArr.Add(preArr[i]);
                        }
                        for (int i = (arr.Length / twoDouble) * twoDouble + twoDouble / 2; i < arr.Length; i++)
                        {
                            rightArr.Add(preArr[i]);
                        }
                        subArr = MergeSortSubProgram(leftArr, rightArr);//最后一组合并
                        for (int i = 0; i < subArr.Count; i++)
                        {
                            tempArr.Add(subArr[i]);
                        }
                        subArr.Clear();
                    }
                }
                else if (arr.Length / twoDouble == 0) //最后一组
                {
                    List<int> leftArr = new List<int>();
                    List<int> rightArr = new List<int>();
                    for (int i = 0; i < twoDouble / 2; i++) {
                        leftArr.Add(preArr[i]);
                    }
                    for (int i = twoDouble / 2; i < arr.Length; i++) {
                        rightArr.Add(preArr[i]);
                    }
                    subArr = MergeSortSubProgram(leftArr, rightArr);//最后一组合并
                    for (int i = 0; i < subArr.Count; i++) {
                        tempArr.Add(subArr[i]);
                    }
                    subArr.Clear();
                }
                
                //preArr = tempArr;//使preArr指向tempArr了
                twoDouble *= 2;
                preArr.Clear();
                for (int x = 0; x < tempArr.Count; x++) {
                    Console.Write(tempArr[x] + "  ");
                    preArr.Add(tempArr[x]);
                }
                Console.WriteLine();
            }
            return tempArr;
        }
        //实现左右2边数组从小到大合并
        List<int> MergeSortSubProgram(List<int> leftArr,List<int> rightArr)
        {
            List<int> tempArr = new List<int>();
            bool flag = true;
            int leftPos = 0, rightPos = 0;

            while (flag) {
                if (leftArr[leftPos] < rightArr[rightPos]) //当左边的数比右边小
                {
                    tempArr.Add(leftArr[leftPos]);
                    leftPos++;
                }
                else {
                    tempArr.Add(rightArr[rightPos]);
                    rightPos++;
                }
                //当其中一组到底之后
                if (leftPos == leftArr.Count || rightPos == rightArr.Count) {
                    flag = false;
                    if (leftPos == leftArr.Count) {
                        for (int i = rightPos; i < rightArr.Count; i++) {
                            tempArr.Add(rightArr[i]);
                        }
                    }
                    else if (rightPos == rightArr.Count) {
                        for (int i = leftPos; i < leftArr.Count; i++) {
                            tempArr.Add(leftArr[i]);
                        }
                    }
                }
            }

            return tempArr;
        }