一、查找算法
需求:从指定列表中查到一个元素
先定义一个列表,需要查到的元素是 105
l = [1,3,4,6,10,33,36,45,49, 66, 77, 78, 79, 90, 96, 105, 312, 644, 647]
1、顺序查找(从头到尾查找,查到就停止,效率低)
def fun1(l, num): n = 0 for i in l: n += 1 print ("count: ", n) if i == num: return l.index(i) return -1
2、二分查找,也叫拆半查找(要求序列必须是顺序的,会将被查找元素先与序列最中间的元素比较,如果小于中间元素,则向左半部分查找,否则向右半部分查找,递归下去。效率高,平均性能好)
def fun2(l, num): n = 0 low = 0 hight = len(l)-1 while low <= hight: n += 1 mid = (low+hight)//2 print ("count: ", n) if num == l[mid]: return mid elif num < l[mid]: hight = mid - 1 else: low = mid + 1 return -1
两者输出比较,顺序查找算法用了16次查到该元素,二分查找算法只用了4次,差距明显
count: 1 count: 2 count: 3 count: 4 count: 5 count: 6 count: ... count: 15 count: 16 15 count: 1 count: 2 count: 3 count: 4 15