Intermediate Java - Fall 2019

24 - Coding challenges and interview questions

Michele

Goals

  • Learn about the coding interview
  • Go through simple coding tasks examples
  • Learn where and how you can get better at it

Examples

1. Reverting a string

Print out a string in reverse order.

Examples

Input: Hello World
Ourpur: dlroW olleH

Input: This is crazy
Output: yzarc si sihT


2. Most frequent element in an array (from https://www.geeksforgeeks.org/frequent-element-array/)

Given an array, find the most frequent element in it. If there are multiple elements that appear maximum number of times, print any one of them.

Examples

Input : arr[] = {1, 3, 2, 1, 4, 1}
Output : 1
 
Input : arr[] = {10, 20, 10, 20, 30, 20, 20}
Output : 20

😎 Toggle Solution 
//Java program to find the most frequent element 
//in an array 
import java.util.HashMap; 
import java.util.Map; 
import java.util.Map.Entry; 
  
class GFG { 
      
    static int mostFrequent(int arr[], int n) 
    { 
          
        // Insert all elements in hash 
        Map<Integer, Integer> count = new HashMap<Integer, Integer>(); 
          
        for(int i = 0; i < n; i++) 
        { 
            int key = arr[i]; 
            if(count.containsKey(key)) 
            { 
                int freq = count.get(key); 
                freq++; 
                count.put(key, freq); 
            } 
            else
            { 
                count.put(key, 1); 
            } 
        } 
          
        // find max frequency. 
        int max_count = 0, res = -1; 
          
        for(Entry<Integer, Integer> val : count.entrySet()) 
        { 
            if (max_count < val.getValue()) 
            { 
                res = val.getKey(); 
                max_count = val.getValue(); 
            } 
        } 
          
        return res; 
    } 
      
    // Driver code 
    public static void main (String[] args) { 
          
        int arr[] = {1, 5, 2, 1, 3, 2, 1}; 
        int n = arr.length; 
          
        System.out.println(mostFrequent(arr, n)); 
    } 
}


Questions Marks (from https://www.coderbyte.com/editor/Questions%20Marks:Java)

Have the function QuestionsMarks(str) take the str string parameter, which will contain single digit numbers, letters, and question marks, and check if there are exactly 3 question marks between every pair of two numbers that add up to 10. If so, then your program should return the string true, otherwise it should return the string false. If there aren't any two numbers that add up to 10 in the string, then your program should return false as well.

For example: if str is "arrb6???4xxbl5???eee5" then your program should return true because there are exactly 3 question marks between 6 and 4, and 3 question marks between 5 and 5 at the end of the string.

Examples

Input: "aa6?9"
Output: false

Input: "acc?7??sss?3rr1??????5"
Output: true

😎 Toggle Solution 
import java.util.*; 
import java.io.*;

class Main {

  // by no means the best solution!!!
  public static boolean QuestionsMarks(String str) {
    boolean status = true;
    boolean pairFound = false;
    
    Integer first = null;
    int count = 0;
    
    for (char c : str.toCharArray()) {
      if (c == '?') { count += 1; }
      else if (Character.isLetter(c)) {
        continue;
      } else if(Character.isDigit(c)) {
        Integer current = Character.getNumericValue(c);
        if (first == null) { count = 0; first = current; }
        else {
          int tot = current + first;
          if (tot == 10) {
            pairFound = true;
            if (count != 3) { status = false; } 
          }
          first = current;
          count = 0;
        }
      }
    }
    
    if (pairFound == false) status = false;
    return status;
  }

  public static void main (String[] args) {  
    // keep this function call here     
    Scanner s = new Scanner(System.in);
    System.out.print(QuestionsMarks(s.nextLine())); 
  }
}

Additional Resources

Interactive code challenges

Other resources

  • https://www.softwaretestinghelp.com/java-coding-interview-programs/
  • https://javarevisited.blogspot.com/2017/07/top-50-java-programs-from-coding-Interviews.html
Last Updated: 12/2/2019, 3:14:43 PM

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