Explore algorithmic challenges in string manipulation, linked lists, arrays, queues, and search algorithms, ideal for coding interview preparation.

Become a Java Developer

This module tackles various algorithmic problems, including string manipulation, linked lists, arrays, and queue implementations, as well as search algorithms. Each problem is paired with a detailed solution explanation, preparing you for grokking the coding interview.

Cracking the Coding Interview

# 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:

"lazy dog a over fox jumped brown quick The"

"dog lazy over a jumped fox brown quick The"

"dog lazy jumped jumped fox brown quick The"

"dog lazy a over jumped fox brown quick The"

What is the output if the following sentence is given as an input?

“The quick brown fox jumped over a lazy dog”.


What is the output if the following sentence is given as an input?
“The quick brown fox jumped over a lazy dog”.

What is the output if the following sentence is given as an input?

“She sells seashells on the seashore”.

What is the output if the following sentence is given as an input?
“She sells seashells on the seashore”.

"practice problems to improve your Coding"

"problems to improve your coding practice"

"to improve your coding practice problems"

"gnidoc ruoy evorpmi ot smelborp ecitcarp"

What is the original string for the provided reversed string?

“Coding your improve to problems practice”.

What is the original string for the provided reversed string?
“Coding your improve to problems practice”.

What is the output if the following sentence is given as an input?

“Reverse the words in a sentence”.

What is the output if the following sentence is given as an input?
“Reverse the words in a sentence”.

Reverse Words in a String

Reverse Words in a String

# 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: `reverseWords`\n- Candidate's submitted solution code: USER_CODE\n- Error: ERROR_DESCRIPTION\n- Failed test case: FAILED_TEST_CASE\n- Coding language: `Java`\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 `reverseWords` 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 `reverseWords`.\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) `reverseWords`. \n- While calculating time complexity, include the time complexity of built-in Java 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) `reverseWords`. \n- While calculating space complexity, include the space complexity of built-in Java 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.

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
 """
 import re

 def reverse_words(sentence):
 sentence = re.sub(' +',' ',sentence.strip())

 sentence = list(sentence)
 str_len = len(sentence)
 
 str_rev(sentence, 0, str_len - 1)
 
 start = 0
 end = 0

 while (start < str_len):
 while end < str_len and sentence[end] != ' ':
 end += 1
 str_rev(sentence, start, end - 1)
 start = end + 1;
 end += 1
 
 return ''.join(sentence)


 # A function that reverses a whole sentence character by character
 def str_rev(_str, start_rev, end_rev):
 while start_rev < end_rev:
 temp = _str[start_rev] 
 _str[start_rev] = _str[end_rev] 
 _str[end_rev] = temp 

 start_rev += 1 
 end_rev -= 1 



 # multiple outputs will be added at each index respectively for a single test_case
 expected_outputs = [] 
 expected = reverse_words(self.__inputs[0])
 actual = self.__actual_outputs[0]
 # store the 1st expected output that should be displayed to the user 
 expected_outputs.append(expected) 
 if expected == actual:
 self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
 else:
 self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)

 return self.__edu_result

import java.util.*;

public class Solution {
    public static String reverseWords(String sentence) {

        // Replace this placeholder return statement with your code
        return "";
    }
}


PrivateTestCases.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1: "We love Python "
    output:
    - 1: "Python love We"
  - name: "testcase 2"
    inputs:
    - 1: "1234 abc XYZ"
    output:
    - 1: "XYZ abc 1234"
  - name: "testcase 3"
    inputs:
    - 1: "You are amazing"
    output:
    - 1: "amazing are You"
  - name: "testcase 4"
    inputs:
    - 1: "Hello     World"
    output:
    - 1: "World Hello"
  - name: "testcase 5"
    inputs:
    - 1: "   Greeting123   "
    output:
    - 1: "Greeting123"

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

def validate_inputs(self) -> None:
 """
 self.__inputs is the list of inputs that are passed as input to the function.
 Store the result using the self.store_result(error_msg, status).
 Return: void
 """
 import re
 # Inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 1
 if len(self.__inputs[0]) < 1 or len(self.__inputs[0]) > 10000:
 self.store_result("Length of sentence should be between 1 and 10000", ValidationFunction.FAIL)
 elif not len(self.__inputs[0].split()) > 0:
 self.store_result("There is at least one word in sentence.", ValidationFunction.FAIL)
 elif not re.match(r'^[a-zA-Z0-9 ]+$', self.__inputs[0]):
 self.store_result("Sentence should contain only English uppercase and lowercase letters, digits, and spaces.", ValidationFunction.FAIL)
 else:
 self.store_result("", ValidationFunction.PASS)

Try to solve the Reverse Words in a String problem.

Problem Solving

Conclusion

Reverse Words in a String

Statement

Examples

Understand the problem

Figure it out!

Try it yourself