Find First Index Of a Number in an Array – Coding Ninjas

First Index Of a Number in an Array

How do you find the first index of an array?

Given an array of length N and an integer x, you need to find and return the first index of integer x present in the array. Return -1 if it is not present in the array.

The first index means, the index of the first occurrence of x in the input array.

Do this recursively. Indexing in the array starts from 0.

Input Format :
Line 1 : An Integer N i.e. size of array
Line 2 : N integers which are elements of the array, separated by spaces
Line 3 : Integer x
Output Format :
first index or -1
Constraints :

1 <= N <= 10^3

Sample Input :
4
9 8 10 8
8
Sample Output :
1

Solution in Java

//Main function

import java.util.Scanner;

public class Runner {
	
	static Scanner s = new Scanner(System.in);
	
	public static int[] takeInput(){
		int size = s.nextInt();
		int[] input = new int[size];
		for(int i = 0; i < size; i++){
			input[i] = s.nextInt();
		}
		return input;
	}
	
	public static void main(String[] args) {
		int[] input = takeInput();
		int x = s.nextInt();
		System.out.println(Solution.firstIndex(input, x));
	}
}

//Solution by technoname.com

public class Solution {

	public static int firstIndex(int input[], int x) {
		return ans(input,x,0);
    }
    
    public static int ans(int input[],int x,int startIndex)
    {
      int n=input.length;
     
        if(startIndex==n)
        {
            return -1;
        }
        if(x==input[startIndex])
        {
            return startIndex;
        }
        return ans(input,x,startIndex+1);
	}

}

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