Python之归并排序

def MergeSort(arrayList):
    arrayLen = len(arrayList)
    # 判断输入参数的正确性
    if arrayLen < 1:
        return []
    # 递归的出口是当分解到长度是1的时候
    if arrayLen == 1:
        return arrayList
    # 获取中间索引值
    middleIndex = (arrayLen >> 1)
    # 递归左半部分
    sortedLeft = MergeSort(arrayList[:middleIndex])
    # 递归右半部分
    sortedRight = MergeSort(arrayList[middleIndex:])
    return MergeCore(sortedLeft,sortedRight)

def MergeCore(leftList,rightList):
    leftIndex = 0
    rightIndex = 0
    # 由于用到多次，length我们自己保存
    leftLen = len(leftList)
    rightLen = len(rightList)
    retList = []
    # 循环比较，直到一个数组比较完毕
    while leftIndex < leftLen and rightIndex < rightLen:
        if leftList[leftIndex] < rightList[rightIndex]:
            retList.append(leftList[leftIndex])
            leftIndex += 1
        else:
            retList.append(rightList[rightIndex])
            rightIndex += 1
    # 将剩余的数组全部放入到返回值的数组中
    if leftIndex < leftLen:
        while leftIndex < leftLen:
            retList.append(leftList[leftIndex])
            leftIndex += 1
    if rightIndex < rightLen:
        while rightIndex < rightLen:
            retList.append(rightList[rightIndex])
            rightIndex += 1
    return retList

if __name__ == '__main__':
     sortedList = MergeSort([14,33,27,10,35,19,42,44,99])
     print(sortedList)