lintcode-easy-Cosine Similarity

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

 

class Solution {
    /**
     * @param A: An integer array.
     * @param B: An integer array.
     * @return: Cosine similarity.
     */
    public double cosineSimilarity(int[] A, int[] B) {
        // write your code here
        if(A == null || B == null)
            return 2.0;
        
        if(A.length != B.length)
            return 2.0;
        
        int num = 0;
        int den1 = 0;
        int den2 = 0;
        
        for(int i = 0; i < A.length; i++){
            num += A[i] * B[i];
            den1 += A[i] * A[i];
            den2 += B[i] * B[i];
        }
        
        if(den1 == 0 || den2 == 0)
            return 2.0;
        
        return num / (Math.sqrt(den1)) / (Math.sqrt(den2));
        
    }
}