LintCode python 小白-简单题-445余弦相识度

题目：Cosine similarity is a measure of similarity between two vectors of an inner product space that measures the cosine of the angle between them. The cosine of 0° is 1, and it is less than 1 for any other angle.

See wiki: Cosine Similarity

Here is the formula:

cosine-similarity

Given two vectors A and B with the same size, calculate the cosine similarity.

Return 2.0000 if cosine similarity is invalid (for example A = [0] and B = [0]).

样例
给出 A = [1, 2, 3], B = [2, 3 ,4].返回 0.9926.

给出 A = [0], B = [0].返回 2.0000

思路：主要注意sqrt函数的使用时，必须调用 import math，lintcode可以直接用math.sqrt(x). 其实也可以用pow(x,0.5)进行开平方。
代码：

class Solution:    """    @param A: An integer array.    @param B: An integer array.    @return: Cosine similarity.    """    def cosineSimilarity(self, A, B):        # write your code here        if A==0 or sum(A)==0 or A==[]:            return 2        x=0        y=0        z=0        for i in range(len(A)):            x=x+A[i]*B[i]            y=y+pow(A[i],2)            z=z+pow(B[i],2)        return x/(math.sqrt(y)*math.sqrt(z))