FB面经Prepare: Dot Product

Conduct Dot Product of two large Vectors

1. two pointers

2. hashmap

3. 如果没有额外空间，如果一个很大，一个很小，适合scan小的，并且在大的里面做binary search

package fb;

public class DotProduct {
    
    public int dotPro(int[][] v1, int[][] v2) {
        int[][] shortV;
        int[][] longV;
        if (v1.length < v2.length) {
            shortV = v1;
            longV = v2;
        }
        else {
            shortV = v2;
            longV = v1;
        }
        
        int res = 0;
        for (int i=0; i<shortV.length; i++) {
            int shortIndex = shortV[i][0];
            int shortValue = shortV[i][1];
            int longSeq = binarySearch(longV, shortIndex);
            if (longSeq >= 0) {
                res += shortValue * longV[longSeq][1];
            }
        }
        return res;
    }
    
    public int binarySearch(int[][] arr, int target) {
        int l=0, r=arr.length-1;
        while (l <= r) {
            int m = (l+r)/2;
            if (arr[m][0] == target) return m;
            else if (arr[m][0] < target) l = m + 1;
            else r = m - 1;
        }
        return -1;
    }
    

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        DotProduct sol = new DotProduct();
        int[][] v2 = new int[][]{{0,2},{1,3},{5,2},{7,1},{10,1}};
        int[][] v1 = new int[][]{{1,6},{7,2}};
        int res = sol.dotPro(v1, v2);
        System.out.println(res);
    }

}