LeetCode 1570: Dot Product of Two Sparse Vectors Solution

Master LeetCode problem 1570 (Dot Product of Two Sparse Vectors), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1570. Dot Product of Two Sparse Vectors

Medium

Array Hash Table Two Pointers Design

Problem Explanation

Explanation

To compute the dot product of two sparse vectors efficiently, we can store only the non-zero elements of the vectors along with their indices. Then, we can iterate over these non-zero elements and multiply the corresponding elements from both vectors. Finally, we sum up these products to get the dot product.

The time complexity of this approach is O(n) where n is the number of non-zero elements in the vectors, as we only iterate over the non-zero elements. The space complexity is also O(n) to store the non-zero elements and their indices.

Solution Code

class SparseVector {
    Map<Integer, Integer> map;

    SparseVector(int[] nums) {
        map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] != 0) {
                map.put(i, nums[i]);
            }
        }
    }

    public int dotProduct(SparseVector vec) {
        int product = 0;
        for (int i : map.keySet()) {
            if (vec.map.containsKey(i)) {
                product += map.get(i) * vec.map.get(i);
            }
        }
        return product;
    }
}

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