[LintCode] Cosine Similarity

Problem

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:

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]).

Example

Given A = [1, 2, 3], B = [2, 3 ,4].
Return 0.9926.
Given A = [0], B = [0].
Return 2.0000

Solution

class Solution {
    public double cosineSimilarity(int[] A, int[] B) {
        // write your code here
        if (A.length == 0 || B.length == 0 || A.length != B.length) {
            return 2;
        }
        int aa = 0, bb = 0, ab = 0;
        for (int i = 0; i < A.length; i++) {
            aa += A[i]* A[i];
            bb += B[i]* B[i];
            ab += A[i]* B[i];
        }
        if (aa == 0 || bb == 0) return 2;
        return ab / (Math.sqrt(aa) * Math.sqrt(bb));
    }
}