归并、快排、二分查找

归并

def MergeSort(lists):
    if len(lists) <= 1:
        return lists
    num = int( len(lists) / 2 )
    left = MergeSort(lists[:num])
    right = MergeSort(lists[num:])
    return Merge(left, right)
def Merge(left,right):
    r, l=0, 0
    result=[]
    while l<len(left) and r<len(right):
        if left[l] <= right[r]:
            result.append(left[l])
            l += 1
        else:
            result.append(right[r])
            r += 1
    result += list(left[l:])
    result += list(right[r:])
    return result
print MergeSort([1, 2, 3, 4, 5, 6, 7, 90, 21, 23, 45])

快排

def quick_sort(data):    
    """快速排序"""    
    if len(data) >= 2:  # 递归入口及出口        
        mid = data[len(data)//2]  # 选取基准值，也可以选取第一个或最后一个元素        
        left, right = [], []  # 定义基准值左右两侧的列表        
        data.remove(mid)  # 从原始数组中移除基准值        
        for num in data:            
            if num >= mid:                
                right.append(num)            
            else:                
                left.append(num)        
        return quick_sort(left) + [mid] + quick_sort(right)    
    else:        
        return data
 
# 示例：
array = [2,3,5,7,1,4,6,15,5,2,7,9,10,15,9,17,12]
print(quick_sort(array))

二分查找

又叫折半查找，即每次从中间开始，根本要查找的值与中间值做对比，依次缩小查找范围

def bin_search(data_list, val):    
    low = 0                         # 最小数下标    
    high = len(data_list) - 1       # 最大数下标    
    while low <= high:        
        mid = (low + high) // 2     # 中间数下标        
        if data_list[mid] == val:   # 如果中间数下标等于val, 返回            
            return mid        
        elif data_list[mid] > val:  # 如果val在中间数左边, 移动high下标            
            high = mid - 1        
        else:                       # 如果val在中间数右边, 移动low下标            
            low = mid + 1    
    return # val不存在, 返回None
ret = bin_search(list(range(1, 10)), 3)
print(ret)