Sparse matrix multiplication done

Author: rampatra

src/main/java/com/leetcode/arrays/SparseMatrixMultiplication.java

@@ -0,0 +1,87 @@
+package com.leetcode.arrays;
+
+import java.util.Arrays;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * Level: Medium
+ * Link: https://leetcode.com/problems/sparse-matrix-multiplication/
+ * Description:
+ * Given two sparse matrices A and B, return the result of AB.
+ *
+ * You may assume that A's column number is equal to B's row number.
+ *
+ * Example:
+ *
+ * Input:
+ *
+ * A = [
+ *   [ 1, 0, 0],
+ *   [-1, 0, 3]
+ * ]
+ *
+ * B = [
+ *   [ 7, 0, 0 ],
+ *   [ 0, 0, 0 ],
+ *   [ 0, 0, 1 ]
+ * ]
+ *
+ * Output:
+ *
+ *      |  1 0 0 |   | 7 0 0 |   |  7 0 0 |
+ * AB = | -1 0 3 | x | 0 0 0 | = | -7 0 3 |
+ *                   | 0 0 1 |
+ *
+ * @author rampatra
+ * @since 2019-08-09
+ */
+public class SparseMatrixMultiplication {
+
+    /**
+     * Time Complexity: O(Arow * Acol * Bcol)
+     * Space Complexity: O(Arow * Bcol)
+     *
+     * @param A
+     * @param B
+     * @return
+     */
+    public static int[][] multiply(int[][] A, int[][] B) {
+        int[][] AB = new int[A.length][B[0].length];
+
+        for (int Bcol = 0; Bcol < B[0].length; Bcol++) {
+            for (int Arow = 0; Arow < A.length; Arow++) {
+                int sum = 0;
+                for (int Acol = 0; Acol < A[0].length; Acol++) {
+                    sum += A[Arow][Acol] * B[Acol][Bcol];
+                }
+                AB[Arow][Bcol] = sum;
+            }
+        }
+
+        return AB;
+    }
+
+    public static void main(String[] args) {
+        assertEquals(Arrays.deepToString(new int[][]{
+                {7, 0, 0},
+                {-7, 0, 3}
+        }), Arrays.deepToString(multiply(new int[][]{
+                {1, 0, 0},
+                {-1, 0, 3}
+        }, new int[][]{
+                {7, 0, 0},
+                {0, 0, 0},
+                {0, 0, 1}
+        })));
+
+        assertEquals(Arrays.deepToString(new int[][]{
+                {0}
+        }), Arrays.deepToString(multiply(new int[][]{
+                {0, 1}
+        }, new int[][]{
+                {1},
+                {0}
+        })));
+    }
+}