Oct 8, 2025
diff --git a/Dynamic-Programming/MatrixMultiplication.js b/Dynamic-Programming/MatrixMultiplication.js
 /*
 Wikipedia -> https://en.wikipedia.org/wiki/Matrix_multiplication

 Q. -> Given two matrices `A` and `B`, find the product of both matrices.
 Matrix multiplication is only possible when the number of columns in A equals the number of rows in B.

 Formula ->
 If A is of size (n × m) and B is of size (m × p),
 then the result matrix C will be of size (n × p),
 where each element C[i][j] = Σ (A[i][k] * B[k][j]) for k = 0 to m-1.

 Algorithm details ->
 time complexity - O(n * m * p)
 space complexity - O(n * p)
 */

 const matrixMultiplication = (A, B) => {
  const n = A.length;           // rows in A
  const m = A[0].length;        // columns in A (and rows in B)
  const p = B[0].length;        // columns in B

  // Check if multiplication is possible
  if (m !== B.length) {
    throw new Error('Matrix multiplication not possible: columns of A must equal rows of B');
  }

  // Create a result matrix filled with 0s of size (n × p)
  const result = new Array(n).fill(0).map(() => new Array(p).fill(0));

  /*
    Perform matrix multiplication:
    For each row in A and column in B,
    multiply and sum corresponding elements.
  */
  for (let i = 0; i < n; i++) {
    for (let j = 0; j < p; j++) {
      let sum = 0;
      for (let k = 0; k < m; k++) {
        sum += A[i][k] * B[k][j];
      }
      result[i][j] = sum;
    }
  }

  return result;
 };

 // Example usage
 const A = [
  [1, 2, 3],
  [4, 5, 6]
 ];

 const B = [
  [7, 8],
  [9, 10],
  [11, 12]
 ];

 console.log(matrixMultiplication(A, B));
 // Output: [ [ 58, 64 ], [ 139, 154 ] ]

 export { matrixMultiplication };
diff --git a/Dynamic-Programming/tests/MatrixMultiplication.test.js b/Dynamic-Programming/tests/MatrixMultiplication.test.js
 import { matrixMultiplication } from '../MatrixMultiplication'

 test('matrixMultiplication([[1,2,3],[4,5,6]], [[7,8],[9,10],[11,12]]) => [[58,64],[139,154]]', () => {
  const A = [
    [1, 2, 3],
    [4, 5, 6]
  ]
  const B = [
    [7, 8],
    [9, 10],
    [11, 12]
  ]
  const res = matrixMultiplication(A, B)
  expect(res).toEqual([
    [58, 64],
    [139, 154]
  ])
 })

 test('matrixMultiplication([[2,4],[3,4]], [[1,2],[1,3]]) => [[6,16],[7,18]]', () => {
  const A = [
    [2, 4],
    [3, 4]
  ]
  const B = [
    [1, 2],
    [1, 3]
  ]
  const res = matrixMultiplication(A, B)
  expect(res).toEqual([
    [6, 16],
    [7, 18]
  ])
 })

 test('matrixMultiplication([[1,2],[3,4]], [[5,6],[7,8]]) => [[19,22],[43,50]]', () => {
  const A = [
    [1, 2],
    [3, 4]
  ]
  const B = [
    [5, 6],
    [7, 8]
  ]
  const res = matrixMultiplication(A, B)
  expect(res).toEqual([
    [19, 22],
    [43, 50]
  ])
 })

 test('matrixMultiplication([[1]], [[2]]) => [[2]]', () => {
  const A = [[1]]
  const B = [[2]]
  const res = matrixMultiplication(A, B)
  expect(res).toEqual([[2]])
 })

 test('throws error when matrices cannot be multiplied', () => {
  const A = [
    [1, 2, 3],
    [4, 5, 6]
  ]
  const B = [
    [1, 2],
    [3, 4]
  ]
  expect(() => matrixMultiplication(A, B)).toThrow(
    'Matrix multiplication not possible: columns of A must equal rows of B'
  )
 })
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,63 @@
		/*
		Wikipedia -> https://en.wikipedia.org/wiki/Matrix_multiplication

		Q. -> Given two matrices `A` and `B`, find the product of both matrices.
		Matrix multiplication is only possible when the number of columns in A equals the number of rows in B.

		Formula ->
		If A is of size (n × m) and B is of size (m × p),
		then the result matrix C will be of size (n × p),
		where each element C[i][j] = Σ (A[i][k] * B[k][j]) for k = 0 to m-1.

		Algorithm details ->
		time complexity - O(n * m * p)
		space complexity - O(n * p)
		*/

		const matrixMultiplication = (A, B) => {
		const n = A.length; // rows in A
		const m = A[0].length; // columns in A (and rows in B)
		const p = B[0].length; // columns in B

		// Check if multiplication is possible
		if (m !== B.length) {
		throw new Error('Matrix multiplication not possible: columns of A must equal rows of B');
		}

		// Create a result matrix filled with 0s of size (n × p)
		const result = new Array(n).fill(0).map(() => new Array(p).fill(0));

		/*
		Perform matrix multiplication:
		For each row in A and column in B,
		multiply and sum corresponding elements.
		*/
		for (let i = 0; i < n; i++) {
		for (let j = 0; j < p; j++) {
		let sum = 0;
		for (let k = 0; k < m; k++) {
		sum += A[i][k] * B[k][j];
		}
		result[i][j] = sum;
		}
		}

		return result;
		};

		// Example usage
		const A = [
		[1, 2, 3],
		[4, 5, 6]
		];

		const B = [
		[7, 8],
		[9, 10],
		[11, 12]
		];

		console.log(matrixMultiplication(A, B));
		// Output: [ [ 58, 64 ], [ 139, 154 ] ]

		export { matrixMultiplication };
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,71 @@
		import { matrixMultiplication } from '../MatrixMultiplication'

		test('matrixMultiplication([[1,2,3],[4,5,6]], [[7,8],[9,10],[11,12]]) => [[58,64],[139,154]]', () => {
		const A = [
		[1, 2, 3],
		[4, 5, 6]
		]
		const B = [
		[7, 8],
		[9, 10],
		[11, 12]
		]
		const res = matrixMultiplication(A, B)
		expect(res).toEqual([
		[58, 64],
		[139, 154]
		])
		})

		test('matrixMultiplication([[2,4],[3,4]], [[1,2],[1,3]]) => [[6,16],[7,18]]', () => {
		const A = [
		[2, 4],
		[3, 4]
		]
		const B = [
		[1, 2],
		[1, 3]
		]
		const res = matrixMultiplication(A, B)
		expect(res).toEqual([
		[6, 16],
		[7, 18]
		])
		})

		test('matrixMultiplication([[1,2],[3,4]], [[5,6],[7,8]]) => [[19,22],[43,50]]', () => {
		const A = [
		[1, 2],
		[3, 4]
		]
		const B = [
		[5, 6],
		[7, 8]
		]
		const res = matrixMultiplication(A, B)
		expect(res).toEqual([
		[19, 22],
		[43, 50]
		])
		})

		test('matrixMultiplication([[1]], [[2]]) => [[2]]', () => {
		const A = [[1]]
		const B = [[2]]
		const res = matrixMultiplication(A, B)
		expect(res).toEqual([[2]])
		})

		test('throws error when matrices cannot be multiplied', () => {
		const A = [
		[1, 2, 3],
		[4, 5, 6]
		]
		const B = [
		[1, 2],
		[3, 4]
		]
		expect(() => matrixMultiplication(A, B)).toThrow(
		'Matrix multiplication not possible: columns of A must equal rows of B'
		)
		})