算法（python实现）First

• 排序算法（选择、冒泡和归并）和查找算法（顺序和折半）

  def select_sort(origin_items, comp=lambda x, y: x < y):
      """简单选择排序"""
      items = origin_items[:]
      for i in range(len(items) - 1):
          min_index = i
          for j in range(i + 1, len(items)):
              if comp(items[j], items[min_index]):
                  min_index = j
          items[i], items[min_index] = items[min_index], items[i]
      return items

  def bubble_sort(origin_items, comp=lambda x, y: x > y):
      """高质量冒泡排序(搅拌排序)"""
      items = origin_items[:]
      for i in range(len(items) - 1):
          swapped = False
          for j in range(i, len(items) - 1 - i):
              if comp(items[j], items[j + 1]):
                  items[j], items[j + 1] = items[j + 1], items[j]
                  swapped = True
          if swapped:
              swapped = False
              for j in range(len(items) - 2 - i, i, -1):
                  if comp(items[j - 1], items[j]):
                      items[j], items[j - 1] = items[j - 1], items[j]
                      swapped = True
          if not swapped:
              break
      return items
  
  

  def merge_sort(items, comp=lambda x, y: x <= y):
      """归并排序(分治法)"""
      if len(items) < 2:
          return items[:]
      mid = len(items) // 2
      left = merge_sort(items[:mid], comp)
      right = merge_sort(items[mid:], comp)
      return merge(left, right, comp)
  
  
  def merge(items1, items2, comp):
      """合并(将两个有序的列表合并成一个有序的列表)"""
      items = []
      index, index2 = 0, 0
      while index1 < len(items1) and index2 < len(items2):
          if comp(items1[index1], items2[index2]):
              items.append(items1[index1])
              index1 += 1
          else:
              items.append(items2[index2])
              index2 += 1
      items += items1[index1:]
      items += items2[index2:]
      return items

  def seq_search(items, key):
      """顺序查找"""
      for index, item in enumerate(items):
          if item == key:
              return index
      return -1

  def bin_search(items, key):
      """折半查找"""
      start, end = 0, len(items) - 1
      while start <= end:
          mid = (start + end) // 2
          if key > items[mid]:
              start = mid + 1
          elif key < items[mid]:
              end = mid - 1
          else:
              return mid
      return -1