Learn and practice the Stacks, and Matrices patterns to solve coding interview problems.

Speedrun the Apple Coding Interview: Top Problems in JavaScript

Interviewers want to be sure that the candidate is comfortable manipulating linked lists, arrays, and data structures based on them, such as stacks and matrices. This module will provide the practice you need to review the concepts and techniques needed to solve common problems involving these data structures.

Basic Data Structures

# Statement

Given an $n \times n$ matrix, rotate the matrix 90 degrees clockwise. The performed rotation should be in place, i.e., the given matrix is modified directly without allocating another matrix. 

>**Note:** The function should only return the modified input matrix.

**Constraints:**

- `matrix.length` $=$ `matrix[i].length`
- $1 \leq$ `matrix.length` $\leq 20$
- $-10^3 \leq$ `matrix[i][j]` $\leq 10^3$

# Examples

# Understand the problem

Let’s take a moment to make sure you've correctly understood the problem. The quiz below helps you check if you're solving the correct problem:

[[8, 8, 9],\
&nbsp;&nbsp;[8, 4, 3],\
&nbsp;&nbsp;[8, 6, 2]]

[[8, 8, 8],\
&nbsp;&nbsp;[6, 4, 8],\
&nbsp;&nbsp;[2, 3, 9]]

[[9, 3, 2],\
&nbsp;&nbsp;[8, 4, 6],\
&nbsp;&nbsp;[8, 8, 8]]

[[8, 8, 9],\
&nbsp;&nbsp;[8, 6, 2],\
&nbsp;&nbsp;[8, 4, 3]]

What is the output if the following matrix is given as input?

matrix = [[2, 6, 8],\
                      &nbsp;&nbsp;&nbsp;&nbsp;[3, 4, 8],\
                     &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[9, 8, 8]]

What is the output if the following matrix is given as input?
matrix = [[2, 6, 8], 
                  [3, 4, 8], 
                  [9, 8, 8]]

&nbsp;[[3, 4, 8, 7],\
&nbsp;&nbsp;[6, 4, 9, 1],\
&nbsp;&nbsp;[3, 7, 7, 7],\
&nbsp;&nbsp;[3, 3, 9, 5]]


&nbsp;[[5, 9, 3, 3],\
&nbsp;&nbsp;[7, 7, 7, 3],\
&nbsp;&nbsp;[1, 9, 4, 6],\
&nbsp;&nbsp;[7, 8, 4, 3]]

&nbsp;[[3, 4, 8, 7],\
&nbsp;&nbsp;[6, 9, 7, 1],\
&nbsp;&nbsp;[3, 4, 7, 7],\
&nbsp;&nbsp;[3, 3, 9, 5]]

&nbsp;[[3, 4, 8, 7],\
&nbsp;&nbsp;[6, 7, 7, 1],\
&nbsp;&nbsp;[3, 9, 4, 7],\
&nbsp;&nbsp;[3, 3, 9, 5]]

What is the output if the following matrix is given as input?

matrix = [[7, 1, 7, 5],\
                      &nbsp;&nbsp;&nbsp;&nbsp;[8, 9, 7, 9],\
                     &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[4, 4, 7, 3],\
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[3, 6, 3, 3]]

What is the output if the following matrix is given as input?
matrix = [[7, 1, 7, 5], 
                  [8, 9, 7, 9], 
                  [4, 4, 7, 3], 
                  [3, 6, 3, 3]]

&nbsp;[[5, 4, 3, 2, 1],\
&nbsp;&nbsp;[5, 3, 3, 6, 3],\
&nbsp;&nbsp;[3, 3, 4, 4, 7],\
&nbsp;&nbsp;[9, 9, 8, 7, 9],\
&nbsp;&nbsp;[9, 5, 7, 7, 1]]


&nbsp;[[9, 9, 3, 5, 5],\
&nbsp;&nbsp;[5, 9, 3, 3, 4],\
&nbsp;&nbsp;[7, 8, 4, 3, 3],\
&nbsp;&nbsp;[7, 7, 4, 6, 2],\
&nbsp;&nbsp;[1, 9, 7, 3, 1]]


&nbsp;[[1, 3, 7, 9, 1],\
&nbsp;&nbsp;[2, 6, 4, 7, 7],\
&nbsp;&nbsp;[3, 3, 4, 8, 7],\
&nbsp;&nbsp;[5, 5, 3, 9, 9],\
&nbsp;&nbsp;[4, 3, 3, 9, 5]]


&nbsp;[[1, 3, 7, 9, 1],\
&nbsp;&nbsp;[2, 6, 4, 7, 7],\
&nbsp;&nbsp;[3, 3, 4, 8, 7],\
&nbsp;&nbsp;[4, 3, 3, 9, 5],\
&nbsp;&nbsp;[5, 5, 3, 9, 9]]


What is the output if the following matrix is given as input?

matrix = [[1, 7, 7, 5, 9],\
                      &nbsp;&nbsp;&nbsp;&nbsp;[9, 7, 8, 9, 9],\
                     &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[7, 4, 4, 3, 3],\
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[3, 6, 3, 3, 5],\
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[1, 2, 3, 4, 5]]


What is the output if the following matrix is given as input?
matrix = [[1, 7, 7, 5, 9], 
                  [9, 7, 8, 9, 9], 
                  [7, 4, 4, 3, 3], 
                  [3, 6, 3, 3, 5], 
                  [1, 2, 3, 4, 5]]

Rotate Image

Rotate Image

# Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.


# Try it yourself

Implement your solution in the following coding playground:

# Quick Fix\nYou are Edward, a Senior Software Engineer who specializes in coding interview patterns, data structures and algorithms, and is great at debugging issues in code.\n\n- Edward, please keep in mind that you do not have to print the data of the placeholders. Also, do not mention anything about yourself.\n\nEdward, you are given the following data in the placeholders:\n- Function name: `rotateImage`\n- Candidate's submitted solution code: USER_CODE\n- Error: ERROR_DESCRIPTION\n- Failed test case: FAILED_TEST_CASE\n- Coding language: `JavaScript`\n\n- Edward, your task is to understand the type of error that is occurring in the coding language provided.\n- Once you've understood the error as per the error’s description, and why the test case failed, you will suggest how the candidate can improve their solution code to fix the error.\n- Edward, you will not give the corrected code, just a hint on what the error tells, and how to fix it.\n- Edward, please limit your response strictly to 100 words. No more words than the limit.

# Review Code\nEdward, your current task is to review the `rotateImage` function(s) and the other function(s) invoked in it/them.\n\n-Take your time and review the candidate's solution code.\n- Do not review any extra/helper files or functions not invoked in the solution function `rotateImage`.\n- Do not review the code of data structure objects instantiated like a binary tree, linked list, trie, union find, etc., in the solution functions. Just review the solution/algorithm function of the problem. \n- Also, if the solution code doesn’t use the coding pattern stated above, then please encourage the candidate to reattempt the problem using that pattern corectly.

# Review time complexity\n- Please provide a brief time complexity analysis of the function(s) `rotateImage`. \n- While calculating time complexity, include the time complexity of built-in JavaScript functions invoked by the code. \n- The answer should be to the point in approximately 60 words.

# Review space complexity\n- Please provide a brief space complexity analysis of the function(s) `rotateImage`. \n- While calculating space complexity, include the space complexity of built-in JavaScript functions invoked by the code. \n- Do not include the space used for the input parameters and the space used for just returning an output (not used as a scratch space). \n- The answer should be to the point in approximately 60 words.

TwoDArray

import DataStructure from "../../data/DataStructure.js";

// className: TwoDArray
export default class TwoDArray extends DataStructure {
  constructor() {
    super();
    // class attributes
  }

  // throw parsing errors for incorrect test case format
  onError(data) {
    process.stderr.write("Parsing Error: " + data + " in TwoDArray is not parsable");
    process.exit();
  }

  toString = function () {
    // override print() for your data structure
  };

  // return value will be passed to user program
  construct(value, typeOfArr) {
    // parse test case in json string 'value' to your desired data structure
    return JSON.parse(JSON.stringify(value))
  }

  // input param contains return value of user program
  traverse(input, typeOfArr) {
    // convert your data structure 'input' to a json string representing a test case output
    return input
  }
}

def evaluate_results(self) -> object:
        """
        self.__inputs is the list of inputs that are passed as input to function
        self.__actual_output is a list of outputs that is produced by the learner's code
        return : self.__edu__result object
        """

        def rotate_image_eval(matrix):
            n = len(matrix)
            for row in range(n // 2):
                for col in range(row, n - row - 1):
                    matrix[row][col], matrix[col][n - 1 - row] = matrix[col][n - 1 - row], matrix[row][col]
                    matrix[row][col], matrix[n - 1 - row][n - 1 - col] = matrix[n - 1 - row][n - 1 - col], matrix[row][col]
                    matrix[row][col], matrix[n - 1 - col][row] = matrix[n - 1 - col][row], matrix[row][col] 
            return matrix

        expected = rotate_image_eval(self.__inputs[0])
        # multiple outputs will be added at each index respectively for a single test_case
        expected_outputs = [] 
        # store the 1st expected output that should be displayed to the user 

        if json.dumps(expected) == json.dumps(self.__actual_outputs[0]):
            expected_outputs.append(expected)
            self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
        else:
            expected_outputs.append(expected)
            self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)

        return self.__edu_result

function rotateImage(matrix){
    
    // Replace this placeholder return statement with your code
    return [[]]
}

export { 
    rotateImage
}

rotate image (1).yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : [[6, 9], [2, 7]]
    output: 
    - 1 : [[2, 6], [7, 9]]
  - name: "testcase 2"
    inputs:
    - 1: [[1]]
    output:
    - 1 : [[1]]
  - name: "testcase 3"
    inputs:
    - 1: [[2, 14, 8], [12, 7, 14], [3, 3, 7]]
    output:
    - 1 : [[3, 12, 2], [3, 7, 14], [7, 14, 8]]
  - name: "testcase 4"
    inputs:
    - 1: [[3, 1, 1, 7], [15, 12, 13, 13], [4, 14, 12, 4], [10, 5, 11, 12]]
    output:
    - 1 : [[10, 4, 15, 3], [5, 14, 12, 1], [11, 12, 13, 1], [12, 4, 13, 7]]
  - name: "testcase 5"
    inputs:
    - 1: [[10, 1, 14, 11, 14], [13, 4, 8, 2, 13], [10, 19, 1, 6, 8], [20, 10, 8, 2, 12], [15, 6, 8, 8, 18]]
    output:
    - 1 : [[15, 20, 10, 13, 10], [6, 10, 19, 4, 1], [8, 8, 1, 8, 14], [8, 2, 6, 2, 11], [18, 12, 8, 13, 14]]

def sum(input_1, input_2):
    return input_1+input_2

def validate_inputs(self) -> None:
 """
 Validate the matrix based on the given constraints.
 Store the result using self.store_result(error_msg, status).
 return: void
 """
 matrix = self.__inputs[0]

 # Conditions to check whether the entered input is correct according to the
 # specified data type in CTW
 def is_valid_2d_array(arr):
 if not isinstance(arr, list) or not all(isinstance(row, list) for row in arr):
 return False # Not a valid 2D array if it's empty or contains non-list elements

 for row in arr:
 if any(elem is None or isinstance(elem, bool) for elem in row):
 return False # Not a valid 2D array if any element in a row is None
 if not all(isinstance(elem, int) for elem in row):
 return False # Not a valid 2D array if any element in a row is not an integer

 return True # Valid 2D array

 if not is_valid_2d_array(matrix):
 self.store_result ("Invalid input: Only 2D integer array is acceptable", ValidationFunction.FAIL)
 elif matrix != [] and len(matrix[0]) == 0:
 self.store_result("Number of rows in the matrix should be in the range 1 <= matrix.length <= 20", ValidationFunction.FAIL)
 elif not(1 <= len(matrix) <= 20):
 self.store_result("Number of rows in the matrix should be in the range 1 <= matrix.length <= 20", ValidationFunction.FAIL)
 elif not all(len(row) == len(matrix) for row in matrix):
 self.store_result("The matrix should be square (number of rows equals number of columns)", ValidationFunction.FAIL)
 elif not all(-10**3 <= value <= 10**3 for row in matrix for value in row):
 self.store_result("Matrix values should be in the range -10^3 ≤ matrix[i][j] ≤ 10^3", ValidationFunction.FAIL)
 else:
 self.store_result("", ValidationFunction.PASS)

Stacks

Matrices

Conclusion

Rotate Image

Statement

Examples

Understand the problem

Figure it out!

Try it yourself