Cosine Similarity 445

Question

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

根据公式写即可。

代码如下：

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 || A.length == 0 || B == null || B.length == 0){
            return 2.0;
        }

        double sumA = 0;
        double sumB = 0;
        for(int i = 0; i < A.length; i++){
            sumA += A[i] * A[i];
            sumB += B[i] * B[i];
        }

        if(sumA == 0 || sumB == 0){
            return 2.0;
        }

        double crossSum = 0;
        for(int i = 0; i < A.length; i++){
            crossSum += A[i] * B[i];
        }

        return crossSum / (Math.sqrt(sumA) * Math.sqrt(sumB));
    }
}