add: rotate image problem, solution, and testing suite (#193)

Merging, thanks.

Author: RyanMcPherson7

TOC.md

@@ -75,6 +75,7 @@
 - [Maximum Product of Three Numbers](src/_Problems_/max-product-of-3-numbers)
 - [Next Greater for Every Element in an Array](src/_Problems_/next-greater-element)
 - [Compose Largest Number](src/_Problems_/compose-largest-number)
+- [Rotate Image](src/_Problems_/rotate-image)
 
 ### Searching
 

src/_Problems_/rotate-image/index.js

@@ -0,0 +1,83 @@
+/*
+  Rotate Image (LeetCode #48)
+
+  - You are given an n x n 2D matrix representing an image, rotate the 
+    image by 90 degrees (clockwise).
+  - You have to rotate the image in-place, which means you have to modify 
+    the input 2D matrix directly. DO NOT allocate another 2D matrix and do 
+    the rotation.
+
+  Example 1:
+
+  1 2 3      7 4 1
+  4 5 6 ---> 8 5 2
+  7 8 9      9 6 3
+
+  - Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
+  - Output: [[7,4,1],[8,5,2],[9,6,3]]
+
+  Example 2: 
+
+  5  1  9  11      15 13 2  5
+  2  4  8  10 ---> 14 3  4  1
+  13 3  6  7       12 6  8  9
+  15 14 12 16      16 7  10 11
+
+  - Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]
+  - Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]
+
+  Constraints:
+  - n == matrix.length == matrix[i].length
+  - 1 <= n <= 20
+  - -1000 <= matrix[i][j] <= 1000
+*/
+
+/* 
+  Solution:
+
+  1. First, take the transpose of the matrix
+    - Example:
+    1 2 3      1 4 7
+    4 5 6 ---> 2 5 8
+    7 8 9      3 6 9
+
+  2. Second, flip the matrix horizontally
+    - Example:
+    1 4 7      7 4 1
+    2 5 8 ---> 8 5 2
+    3 6 9      9 6 3
+
+  3. Problem solved!
+
+  - Solution is O(n) where n is the size (total number of entries) of the 
+    input matrix
+*/
+
+function rotateImage(matrix) {
+  const n = matrix.length;
+
+  // take transpose
+  for (let i = 0; i < n; i++) {
+    for (let j = i; j < n; j++) {
+      const temp = matrix[i][j];
+      matrix[i][j] = matrix[j][i];
+      matrix[j][i] = temp;
+    }
+  }
+
+  // flip horizontally
+  for (let i = 0; i < n; i++) {
+    let left = 0;
+    let right = n - 1;
+
+    while (left < right) {
+      const temp = matrix[i][left];
+      matrix[i][left] = matrix[i][right];
+      matrix[i][right] = temp;
+      left++;
+      right--;
+    }
+  }
+}
+
+module.exports = { rotateImage };

src/_Problems_/rotate-image/rotate-image.test.js

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+const { rotateImage } = require('.');
+
+describe('Rotate Image', () => {
+  it('Should rotate 3x3 matrix elements by 90 degrees', () => {
+    const inputMatrix = [
+      [1, 2, 3],
+      [4, 5, 6],
+      [7, 8, 9],
+    ];
+
+    const expectedMatrix = [
+      [7, 4, 1],
+      [8, 5, 2],
+      [9, 6, 3],
+    ];
+
+    rotateImage(inputMatrix);
+    expect(inputMatrix).toEqual(expectedMatrix);
+  });
+  it('Should rotate 4x4 matrix elements by 90 degrees', () => {
+    const inputMatrix = [
+      [5, 1, 9, 11],
+      [2, 4, 8, 10],
+      [13, 3, 6, 7],
+      [15, 14, 12, 16],
+    ];
+
+    const expectedMatrix = [
+      [15, 13, 2, 5],
+      [14, 3, 4, 1],
+      [12, 6, 8, 9],
+      [16, 7, 10, 11],
+    ];
+
+    rotateImage(inputMatrix);
+    expect(inputMatrix).toEqual(expectedMatrix);
+  });
+  it('Should rotate 5x5 matrix elements by 90 degrees', () => {
+    const inputMatrix = [
+      [1, 2, 3, 4, 5],
+      [6, 7, 8, 9, 10],
+      [11, 12, 13, 14, 15],
+      [16, 17, 18, 19, 20],
+      [21, 22, 23, 24, 25],
+    ];
+
+    const expectedMatrix = [
+      [21, 16, 11, 6, 1],
+      [22, 17, 12, 7, 2],
+      [23, 18, 13, 8, 3],
+      [24, 19, 14, 9, 4],
+      [25, 20, 15, 10, 5],
+    ];
+
+    rotateImage(inputMatrix);
+    expect(inputMatrix).toEqual(expectedMatrix);
+  });
+});