Learn and practice the Cyclic Sort and Topological Sort patterns to solve coding interview problems.

Educative-99 in Java: Accelerate Your Coding Interview Prep

This module will focus on two advanced sorting algorithms, Cyclic Sort and Topological Sort. These are often used in coding interviews as a way to distinguish between average and outstanding candidates. Cyclic Sort may only be used if the input list meets certain criteria, and in those situations, it’s the most efficient sorting algorithm possible. Topological Sort utilizes graph-based algorithms to deal with partially ordered elements. This module teaches us to recognize whether either of these advanced sorting techniques is applicable, as well as how to use them to solve the given problem.

Advanced Sorting Techniques

# Statement

Given an unsorted integer array, `nums`, return the smallest missing positive integer. 
Create an algorithm that runs with an $O(n)$ time complexity and utilizes a constant amount of space.

> **Note:** The smallest missing positive isn't the first positive number that's missing in the range of elements in the input, but the first positive number that’s missing if we start from $1$.


**Constraints:**

- $1 \leq$ `nums.length` $\leq 10^5$

- $-2^{31} \leq$ `nums[i]` $\leq 2^{31} - 1$

## 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:

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

[7, 8, 9, 11, 12]

What is the output if the following array is given as input?
[7, 8, 9, 11, 12]

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

[-1, -2, -3, -4, -5]

What is the output if the following array is given as input?
[-1, -2, -3, -4, -5]

Find the Smallest Missing Positive Number

Find the Smallest Missing Positive Number

import java.util.*;
public class FirstMissing{
   public static int firstMissingPositiveInteger(int[] nums) {

      // Replace this placeholder return statement with your code
      return -1;
   }
}

# 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: `smallestMissingPositiveInteger`\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 `smallestMissingPositiveInteger` 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 `smallestMissingPositiveInteger`.\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) `smallestMissingPositiveInteger`. \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) `smallestMissingPositiveInteger`. \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.

OneDArray

import ds_v1.DataStructure.DataStructure;
import java.util.*;
public class OneDArray extends DataStructure {
 int[] values = {};


 public OneDArray() {
 //values = {};
 }
 

 public OneDArray(int[] val){
 this.values = new int [val.length];
 for(int i =0; i < val.length;i++){
 values[i] = val[i];
 }
 
 }

 public String toString() {
 return Arrays.toString(values);
 }

 @Override
 public OneDArray construct(String new_value, Integer type_of_ds) {
 String new_value1 = new_value.substring(1,new_value.length() - 1);
 String[] string = new_value1.split(",");
 int[] arr = new int[string.length];
 
 for (int i = 0; i < string.length; i++) {
 arr[i] = Integer.valueOf(string[i]);
 }
 return new OneDArray(arr);

 }

 @Override
 public String traverse(Object input, Integer type_of_ds) {
 
 return input.toString();
 }

}

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
 """
 # 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 
 expected_outputs.append(smallest_missing_positive_integer(self.__inputs[0]))

 if json.dumps(smallest_missing_positive_integer(self.__inputs[0])) == json.dumps(self.__actual_outputs[0]):
 self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
 else:
 self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)

 return self.__edu_result

def smallest_missing_positive_integer(nums):
 i = 0
 while i < len(nums):
 correct_spot = nums[i] - 1
 if 0 <= correct_spot < len(nums) and nums[i] != nums[correct_spot]:
 nums[i], nums[correct_spot] = nums[correct_spot], nums[i]
 else:
 i += 1

 for i in range(len(nums)):
 if i + 1 != nums[i]:
 return i + 1
 return len(nums) + 1

public class Main{
 public static int firstMissingPositiveInteger1(OneDArray c) {
    int m = FirstMissing.firstMissingPositiveInteger(c.values);
    return m;
      
 }
}

PrivateTestCases.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : [1, 2, 3, 5]
    output: 
    - 1 : 4
  - name: "testcase 2"
    inputs:
    - 1: [2, 3, 4, 5, 6]
    output:
    - 1 : 1
  - name: "testcase 3"
    inputs:
    - 1 : [-1, -2, -3, -4]
    output: 
    - 1 : 1
  - name: "testcase 4"
    inputs:
    - 1: [55, 22, 52, 100, 1, 3, -5]
    output:
    - 1 : 2
  - name: "testcase 5"
    inputs:
    - 1: [0, -1, -2, -3, 5]
    output:
    - 1 : 1

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 function
 store the result using the self.store_result(error_msg, status)
 return : void
 """
 nums= self.__inputs[0]
 def is_valid_1d_array(arr):
 if not isinstance(arr, list):
 return False # Not a valid 1D array if it's not a list
 
 return all(isinstance(elem, int) and not isinstance(elem, bool) for elem in arr)
 
 if not is_valid_1d_array(nums):
 self.store_result(("Invalid test case."), ValidationFunction.FAIL)
 elif len(nums) < 1 or len(nums) > 10**5 :
 self.store_result ("Input length should be between 1 and 10^5", ValidationFunction.FAIL)
 elif any(value < -2**31 or value >= 2**31 for value in nums):
 self.store_result("All elements in the input set should be between -2^31 and 2^31 - 1", ValidationFunction.FAIL)
 else:
 self.store_result("", ValidationFunction.PASS)

Try to solve the First Missing Positive problem.

Cyclic Sort

Topological Sort

Conclusion

First Missing Positive

Statement

Examples

Understand the problem

Figure it out!

Try it yourself