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SparseVectorDotProduct.java
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SparseVectorDotProduct.java
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package Leetcode;
import java.util.HashMap;
import java.util.Map;
/**
* @author kalpak
*
* Given two sparse vectors, compute their dot product.
*
* Implement class SparseVector:
*
* SparseVector(nums) Initializes the object with the vector nums
* dotProduct(vec) Compute the dot product between the instance of SparseVector and vec
* A sparse vector is a vector that has mostly zero values, you should store the sparse vector efficiently and compute the dot product between two SparseVector.
*
* Follow up: What if only one of the vectors is sparse?
*
* Example 1:
*
* Input: nums1 = [1,0,0,2,3], nums2 = [0,3,0,4,0]
* Output: 8
* Explanation: v1 = SparseVector(nums1) , v2 = SparseVector(nums2)
* v1.dotProduct(v2) = 1*0 + 0*3 + 0*0 + 2*4 + 3*0 = 8
* Example 2:
*
* Input: nums1 = [0,1,0,0,0], nums2 = [0,0,0,0,2]
* Output: 0
* Explanation: v1 = SparseVector(nums1) , v2 = SparseVector(nums2)
* v1.dotProduct(v2) = 0*0 + 1*0 + 0*0 + 0*0 + 0*2 = 0
* Example 3:
*
* Input: nums1 = [0,1,0,0,2,0,0], nums2 = [1,0,0,0,3,0,4]
* Output: 6
*
*
* Constraints:
*
* n == nums1.length == nums2.length
* 1 <= n <= 10^5
* 0 <= nums1[i], nums2[i] <= 100
*/
public class SparseVectorDotProduct {
Map<Integer, Integer> map; // stores the Index and the corresponding element (non-zero)
SparseVectorDotProduct(int[] nums) {
map = new HashMap<>();
for(int i = 0; i < nums.length; i++) {
if(nums[i] != 0)
map.put(i, nums[i]);
}
}
// Return the dotProduct of two sparse vectors
public int dotProduct(SparseVectorDotProduct vec) {
int result = 0;
for(int key : this.map.keySet()) {
if(vec.map.containsKey(key)) {
result += this.map.get(key) * vec.map.get(key);
}
}
return result;
}
public static void main(String[] args) {
SparseVectorDotProduct v1 = new SparseVectorDotProduct(new int[]{1,0,0,2,3});
SparseVectorDotProduct v2 = new SparseVectorDotProduct(new int[]{0,3,0,4,0});
System.out.println("The Dot Product is : " + v1.dotProduct(v2));
}
}