Add matrix exercises (#22)

Author: simonespa

src/algorithms/matrices.ts

@@ -0,0 +1,72 @@
+/**
+ * The assumptions is that the matrices are N x M (either square or rectangular)
+ * The matrices cannot have rows with different sizes.
+ */
+
+export function sum(matrix: number[][]): number {
+  let sum = 0;
+
+  for (let i = 0; i < matrix.length; i += 1) {
+    for (let j = 0; j < matrix[i].length; j += 1) {
+      sum += matrix[i][j];
+    }
+  }
+
+  return sum;
+}
+
+function getShortestLength(matrix: number[][]): number {
+  const rows = matrix.length;
+  const columns = matrix[0].length;
+
+  if (rows < columns) return rows;
+
+  return columns;
+}
+
+export function sumDiagonal(matrix: number[][]): number {
+  let sum = 0;
+  let index = 0;
+
+  const shortestLength = getShortestLength(matrix);
+
+  while (index < shortestLength) {
+    sum += matrix[index][index];
+    index += 1;
+  }
+
+  return sum;
+}
+
+export function sumAntiDiagonal(matrix: number[][]): number {
+  let sum = 0;
+  let index = 0;
+
+  const shortestLength = getShortestLength(matrix);
+
+  while (index < shortestLength) {
+    sum += matrix[index][matrix.length - 1 - index];
+    index += 1;
+  }
+
+  return sum;
+}
+
+export function sumFrame(matrix: number[][]): number {
+  let sum = 0;
+
+  const numberOfRows = matrix.length;
+  const numberOfColumns = matrix[0].length; // assuming every row has the same size
+
+  // scann horizontally: top + bottom
+  for (let index = 0; index < numberOfColumns; index += 1) {
+    sum += matrix[0][index] + matrix[numberOfRows - 1][index];
+  }
+
+  // scan vertically: left + right
+  for (let index = 1; index < numberOfRows - 1; index += 1) {
+    sum += matrix[index][0] + matrix[index][numberOfColumns - 1];
+  }
+
+  return sum;
+}

test/algorithms/matrices.test.ts

@@ -0,0 +1,24 @@
+import { sum, sumDiagonal, sumAntiDiagonal, sumFrame } from 'src/algorithms/matrices';
+
+const matrix = [
+  [7, 3, 1, 0],
+  [9, 6, 4, 5],
+  [1, 9, 5, 4],
+  [6, 8, 2, 3],
+];
+
+test('sum', () => {
+  expect(sum(matrix)).toBe(73);
+});
+
+test('sumDiagonal', () => {
+  expect(sumDiagonal(matrix)).toBe(21);
+});
+
+test('sumAntiDiagonal', () => {
+  expect(sumAntiDiagonal(matrix)).toBe(19);
+});
+
+test('sumFrame', () => {
+  expect(sumFrame(matrix)).toBe(49);
+});