数据结构算法--1 顺序查找二分查找

def linnear_search(li, val):
    for ind, v in enumerate(li):
        if v == val:
            return ind
    else:
        return None

def linear_search(li, val):     # 顺序查找复杂度为O(n)
    for i in range(len(li)):
        if li[i]==val:
            return i
    return

def binary_search(li,val):
    left=0
    right=len(li)-1
    while left<=right:
        mid=(left+right) // 2
        if li[mid]==val:    # 最后会找到mid
            return mid
        elif li[mid]>val:   # mid值大与查找值,就需要去左半侧查找,right指针就改变
            right=mid-1
        else:
            left=mid+1
    else:
        return None