DSA Interview Coding Questions

1] Arrays

1] Find first and second best score Example

Given an array, write a function to get first, second best scores from the array and return it in new array.

Array may contain duplicates.

Example

myArray = {84,85,86,87,85,90,85,83,23,45,84,1,2,0}
firstSecond(myArray) // {90, 87}
Solution:
import java.util.Arrays;
import java.util.Collections;
public class Exercise {
    public static int[] findTopTwoScores(int[] array) {
        int firstHighest = Integer.MIN_VALUE;
        int secondHighest = Integer.MIN_VALUE;
 
        for (int score : array) {
            if (score > firstHighest) {
                secondHighest = firstHighest;
                firstHighest = score;
            } else if (score > secondHighest && score < firstHighest) {
                secondHighest = score;
            }
        }
 
        return new int[]{firstHighest, secondHighest};
    }
}

2] Missing Number from unique element Array
Write Java function called findMissingNumberInArray that takes an integer array containing n-1 unique elements from a range of 1 to n, with one missing number, and returns the missing number.
Example
myArray = {1,2,3,4,6}
findMissingNumberInArray(myArray, 6) // 5
Hint:
Use the formula (n * (n + 1)) / 2 which  calculates the sum of the first n natural numbers.

public class Exercise {
  public static int findMissingNumberInArray(int[] array) {
        int n = array.length + 1;
        int expectedSum = (n * (n + 1)) / 2;
        int actualSum = 0;
 
        for (int number : array) {
            actualSum += number;
        }
 
        return expectedSum - actualSum;
    }
}

2] Find Duplicates Number
Write a function which takes integer array as a parameter and returns a new integer array with unique elements. (remove duplicates)
Example
removeDuplicates({1, 1, 2, 2, 3, 4, 5})
Output : [1, 2, 3, 4, 5]
public class Exercise {
    public static int[] removeDuplicates(int[] array) {
        int n = array.length;
        int[] uniqueArray = new int[n];
        int index = 0;
 
        for (int i = 0; i < n; i++) {
            boolean isDuplicate = false;
            for (int j = i + 1; j < n; j++) {
                if (array[i] == array[j]) {
                    isDuplicate = true;
                    break;
                }
            }
            if (!isDuplicate) {
                uniqueArray[index++] = array[i];
            }
        }
 
        return Arrays.copyOf(uniqueArray, index);
    }
 
}