Recursion for Coding Interviews in Java/

...

/

Find the First Occurrence of a Number in an Array

Find the First Occurrence of a Number in an Array

This lesson will teach you how to find the first occurrence of a number in an array using recursion.

We'll cover the following...

First Occurrence of a Number

When given an array, find the first occurrence of a given number in that array and return the index of that number.

The following illustration explains how to approach this problem.

Implementing the Code

The following code explains how to find the first occurrence of a number in an array.

Experiment with the code by changing the values of array and num to see how it works!

Press + to interact
class ArrayClass {
  private static int firstOccurrence(int[] a, int n, int currentIndex) {
    if (a.length == currentIndex) {
      return -1;
    }
    else if (a[currentIndex] == n) {
        return currentIndex;
    }
    else {
        return firstOccurrence(a, n, currentIndex+1);
    }
  }
  
  public static void main(String[] args) {
    System.out.print("{");
    
    int[] array = {2,3,4,1,7,8,3};
    for (int i = 0; i < array.length; i++) {
      System.out.print(array[i] + " ");
    }
    System.out.println("}");
    
    int num = 3;
    int result = firstOccurrence(array, num, 0);
    System.out.println("The first occurrence of the number " + num + " is at index: " + result);
  }
}

Understanding the Code

The code snippet above can be broken down into two parts ...