445. Cosine Similarity【LintCode java】

Description

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

解题：按照公式计算，对特殊情况进行处理（数组不为空、分母不为0）。代码如下

public 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.length == 0 || B.length == 0)
             return 2.0000;
        int a = 0;
        int b = 0;
        int sum = 0;
        for(int i = 0; i < A.length; i++){
            a = a + A[i] * A[i];
            b = b + B[i] * B[i];
            sum = sum + A[i] * B[i];
        }
        if(a == 0 || b == 0)
            return 2.000;
        return (double)sum / (Math.sqrt(a) * Math.sqrt(b));
    }
}