Most asking JAVA's Interview Question

1. Palindrome in JAVA in given integer.//ex: 121,323 are Palindrome

public static void findPalindromeInt(int num) {
  int temp = num;
  int result = 0, rem;
  while (num > 0) {
    rem = num % 10;
    result = result * 10 + rem;
    num = num / 10;
  }
  if(temp==result)
    System.out.println("Number is Palindrome");
  else
    System.out.println("Number is not Palindrome");
}

2.  Palindrome in JAVA in given String.

private void checkPalindromeStr(String input) {
    String temp = input;
    String sum = "";
    for (int i = input.length() - 1; i >= 0; i--) {
        sum = sum + input.charAt(i);
    }
    if (temp.equalsIgnoreCase(sum)) {
        Log.d("LOG", "Palindrome");    } else {
        Log.d("LOG", "Not palindrome");    }

}

3. Count character repetition in a given string using HashMap.//ex:wwkggdrdw =w3k1g2d2r1

private static void charCount(String input) {
  HashMap<Character, Integer> map = new HashMap<>();
  for (int i = 0; i <= input.length() - 1; i++) {
    if (map.containsKey(input.charAt(i))) {
      map.put(input.charAt(i), map.get(input.charAt(i))+1);
    }else {
      map.put(input.charAt(i),1);
    }
  }
  for (Map.Entry<Character,Integer> entry:map.entrySet()){
    System.out.print(entry.getKey()+""+entry.getValue()+"");
  }
}

4.  Reverse a String using inbuilt function.//ex:raja=ajar

private static void revString(String input){
  StringBuilder result = new StringBuilder(input);
  result.reverse();
  System.out.println(result);
}

5. Reverse a String without using inbuilt function.//ex:Supriya =ayirpus

private static void revString(String input) {
  String temp = "";
  for (int i = input.length() - 1; i >= 0; i--) {
    temp = temp + input.charAt(i);
  }
  System.out.println(temp);
}

6.  Count number of word in given string.////ex:world is world i am world i =world3 is1 i2 am1

private static void countWord(String input) {
  HashMap<String, Integer> map = new HashMap<>();
  String[] str = input.split(" ");
  for (String s : str) {
    if (map.containsKey(s)) {
      map.put(s, map.get(s) + 1);
    } else {
      map.put(s, 1);
    } 
  }
  for (Map.Entry<String, Integer> entry : map.entrySet()) {
    System.out.print(entry.getKey() + "" + entry.getValue() + " ");
  }
}

7. Count number of word in given string Using minimum code.

private void countWord1(String input) {
    Log.d("Word  1  ", "" + new Date().getTime());
    List<String> stringList = new ArrayList<String>(Arrays.asList(input.split(" ")));
    for (String str : new HashSet<>(stringList)) {
        Log.d("Word : ", "" + str + " : Frequency : " + Collections.frequency(stringList, str));
    }
    Log.d("Word 2  ", "" + new Date().getTime());
}

8. Iterate HashMap using while loop.

//iterate HashMap using While and advance for loop.

private void iterateHash() {
    Map<Integer, String> map = new HashMap<>();
    map.put(1, "supriya");
    map.put(3, "saurabh");
    map.put(2, "ankit");
    map.put(4, "navin");
    Iterator iterator = map.entrySet().iterator();
    while (iterator.hasNext()) {
        Map.Entry entry = (Map.Entry) iterator.next();
        Log.d("LOG", "  " + entry.getKey() + "  " + entry.getValue());    }
}

9. Check Prime 

private static void isPrime(int num) {
  int count = 0;
  for (int i = 2; i < num - 1; i++) {
    if (num % i == 0) {
      count++;
    }
  }
  if (count == 0) {
    System.out.println("Prime Number");
  } else {
    System.out.println("Not Prime");
  }
}

10. Fibonacci series.

private static void printFibonacci(int limit) {
  int a, b = 0, c = 1;
  for (int i = 0; i < limit; i++) {
    a = b;
    b = c;
    c = a + b;
    System.out.println(a + "");
  }
}

11. Iterate ArrayList using while loop and for-each loop.

public static void iterateList(){
  List<Integer> list =new ArrayList<>();
  list.add(132);
  list.add(132);
  list.add(342);
  Iterator iterator= list.iterator();
  while (iterator.hasNext()){
    System.out.println(iterator.next()+"");
  }

Iterate ArrayList using for-each loop.

public static void iterateList() {
  List<Integer> list = new ArrayList<>();
  list.add(132);
  list.add(132);
  list.add(342);
  for(Integer num:list){
    System.out.println(num+"");
  }
}

12. Find Dublicate Character in a given String./emmaroopa=emao

public static void findDuplicate(String input) {
  for (int i = 0; i < input.length() - 1; i++) {
    for (int j = i + 1; j < input.length(); j++) {
      if (input.charAt(i) == input.charAt(j)) {
        System.out.println(input.charAt(i));
      }
    }
  }

13. Check Armstrong Number in java.//Armstrong Number :-153 = 1*1*1 + 5*5*5 + 3*3*3 = 153.

private static void findArmstrong(int num) {
  int result = 0, rem, temp = num;
  while (num > 0) {
    rem = num % 10;
    result = result + (rem * rem * rem);
    num = num / 10;
  }
  if (temp == result) {
    System.out.println(result + "");
  }
}

14. Replace all white space in a given string.

private static void replaceSpace(String input) {
  input = input.replaceAll(" ", "");
  input = input.replaceAll("\\s", "");
  //both can be used
  System.out.println(input);
}

15. Factorial in JAVA

private static void findFactorial(int num){
    int fact=1;
    for(int i=1;i<=num;i++){
      fact=fact*i;
    }
    System.out.println(fact+"");
  }
}

Factorial using Recursion :-

private int recusionFactorial(int n) {
    if (n == 0)
        return 1;
    else        return (n * recusionFactorial(n - 1));
}

16. WAP in JAVA to find run length encoding if the input is "wwwaadxxxw" then output should be :- w3a2d1x3w1.

private static void lengthEncoding(String input) {
  int count = 1;
  String output = "";
  for (int i = 0; i < input.length(); i++) {
    while (i < (input.length() - 1) && input.charAt(i) == input.charAt(i + 1)) {
      count++;
      i++;
    }
    output = output + input.charAt(i) + count;
    count = 1;
  }
  System.out.println(output);
}

17. In  a given alphanumeric string return sum of the digit 0-9 that appears in the string ignoring all other character. Ex: ac2bh3fg12mgf32 output :- 2+3+1+2+3+2 = 13

private void sumOfDigit(String input) {
    int sum = 0;
    for (char s : input.toCharArray()) {
        if (Character.isDigit(s)) {
            sum = sum + Character.getNumericValue(s);
        }
    }
    Log.d("supriya", sum+"");
}

18. Find peak element in an array. A peak element is an element if it is not smaller than its neighbours./ Ex:{10,80,15,2,23,90,67,120,3,134,7} output :- 20,90.120,134.

public static void findPeakElement(int[] element) {
  for (int i = 0; i < element.length; i++) {
    while (i < element.length - 1 && element[i] < element[i + 1] && element[i + 1] > element[i + 2]) {
      System.out.println(element[i + 1]);
      i++;
    }
  }
}

19. WAP leader in an array. An element is leader  if it is greater than its its right side of all element.Ex: {16,17,4,3,5,2} output:- 2,5,17.

public static void findLeader(int[] arr) {
  int max = arr[arr.length - 1];
  System.out.println(max);
  for (int i = arr.length - 1; i >= 0; i--) {
    if (arr[i] > max) {
      max = arr[i];
      System.out.println(arr[i]);
    }
  }
}

20. Array of 0's and 1sin random order.Segregate 0s on left side and 1s on right side of the array.Traverse array only once.
input {0,1,1,0,0,1,0,1,0,1,1}
output{0,0,0,0,0,1,1,1,1,1,1}

public static void printZeroOne(int[] arr) {
    int l = 0;
    int r = arr.length - 1;
    while (l < r) {
        while (arr[l] == 0 && l < r) {
            l++;
        }
        while (arr[r] == 1 && l < r) {
            r--;
        }
        if (l < r) {
            int temp;
            temp = arr[l];
            arr[l] = arr[r];
            arr[r] = temp;
        }
    }
    for (int i : arr) {
        System.out.print(i + " ");
    }
}

21. Remove adjacent occurrences of 2 same character in a string.Ex:- if the input string is "abbacca" the output will be empty or if the input is aaaebccb then output will be e.

22. Given array {5,2,1,7,2,3} and another Y. Find all the pairs whose sum is Y.

private void findPair(int[] arr, int num) {
    for (int i = 0; i < arr.length; i++) {
        for (int j = i + 1; j < arr.length; j++) {
            if (arr[i] + arr[j] == num) {
                System.out.print(arr[i] + "," + arr[j]);
                Log.d("supriya", "  " + arr[i] + "," + arr[j]);
            }
        }
    }
}

23. Binary Search .

private static int binarySearch(int[] arr, int num) {
  int l = 0, r = arr.length - 1, mid;
  while (l <= r) {
    mid = l + ((r - l) / 2);
    if (num == arr[mid]) {
      return mid;
    } else if (num < arr[mid]) {
      r = mid - 1;
    } else if (num > arr[mid]) {
      l = mid + 1;
    }
  }
  return -1;
}

In Binary search if duplicate item is available than search the item at very first position.

Ex:- {21,100, 100, 100, 100, 100, 401, 453, 588, 789, 890};

than print the position of 100 at very first position.

private boolean binarySearch(int[] arr, int num) {
    int l = 0;
    int r = arr.length - 1;
    int mid;
    while (l <= r) {
        mid = l + (r - l / 2);
        if (arr[mid] == num) {
            if (arr[mid - 1] == num) {
                l = l - 1;
            } else {
                Log.d("supriya:::  ", mid + "");
                return true;
            }
        }
        if (num > arr[mid]) {
            l = mid + 1;
        }
        if (num < arr[mid]) {
            r = mid - 1;
        }
    }
    return false;
}

24. Binary tree Inorder Traverses.
25.  Binary tree Preorder.
26.  Binary tree Postorder.
27.BFS Algorithm.
28. DFS Algorithm
29. Max heap / Min Heap
30. Print 3rd last element in linked list on one traverse.
31. WAP Write a Java program to check if a vowel is present in a string.

private static void fun(String s) {
  char[] str = s.toCharArray();
  if (s.toLowerCase().matches(".*[aeiou].*")) {
    System.out.print("Vowel present");
  }else
    System.out.print("Not Vowel present");
}

32. WAP to rated the string at there place ex :- {"my","name","is","supriya"}

o/p:- {"ym","eman","si","ayirpus"}

private void revStringAtPlace(String[] strArr) {
    String str = "";
    for (int i = 0; i < strArr.length; i++) {
        for (int j = strArr[i].length() - 1; j >= 0; j--) {
            str = str + strArr[i].charAt(j) + "";
        }
        strArr[i] = str;
    }
    for (String s : strArr) {
        Log.d("supriya", s);
    }
}


32. WAP to  reverse item in a array. int[] arr{1,3,2}; o/p:- 231
public static void arrayRev(int[] arr) {
    int[] temp = new int[arr.length];
    int j = 0;
    for (int i = arr.length - 1; i >= 0; i--) {
        if (j < arr.length) {
            assert temp != null;
            temp[j] = arr[i];
            j++;
        }
    }
    for (int k : temp) {
        Log.d("supriya", k + "");
    }

}

33. WAP to find second Largest from an array.

public static void findSecondHigh(int[] arr) {
    int largest = arr[0];
    int secLargest = arr[0];
    for (int i = 1; i < arr.length; i++) {
        if (arr[i] > largest) {
            secLargest = largest;
            largest = arr[i];
        } else if (arr[i] > secLargest) {
            secLargest = arr[i];
        }
    }
    Log.d("supriya", "Largest ::=" + largest + "   " + "SecondLargest::  " + secLargest);
}
34. WAP to remove all space from a string.
private static void fun(String str){
  System.out.println(str);
  str = str.replaceAll(" ","");
 System.out.println(str);
}
35. WAP to sort an Array.
private static void fun(int[] arr){
  Arrays.sort(arr);
  for (int i:arr)
    System.out.print(i+" ");
}
36. WAP to make pyramid.
   1 
  1 2 
 1 2 3 
1 2 3 4 
private static void fun(int n) {
  for (int i = 1; i < n; i++) {
    for (int j = n - i; j >1; j--) {
      System.out.print(" ");
    }
    for (int j = 1; j <= i; j++) {
      System.out.print(j+" ");
    }
    System.out.println();
  }
}
37. WAP to illustrate merge sort.