Recursive program to linearly search an element in a given array

Given an unsorted array and an element x, search x in the given array. Write recursive C code for this. If the element is not present, return -1. 

Approach: The idea is to compare x with the last element in arr[]. If the element is found at the last position, return it. Else recur searchElement() for remaining array and element x. 

C++

/*
 * Approach : The idea is to compare x with the last element
 * in arr[]. If the element is found at the last position,
 * return it. Else recur searchElement() for remaining array and
 * element x.
 */


#include <iostream>

using namespace std;

// Recursive function to search for x in arr[]
int searchElement(int arr[], int size, int x) {

    size--;

    // Base case (Element not present in the array)
    if (size < 0) {
        return -1;
    }
    // Base case (Element found, return its position)
    if (arr[size] == x) {
        return size;
    }

    // Recursive case
    return searchElement(arr, size, x);

}


// Driver code
int main() {
    int arr[] = {17, 15, 11, 8, 13, 19};
    int size = sizeof(arr) / sizeof(arr[0]);
    int x = 11;
    int idx = searchElement(arr, size, x);
    if (idx != -1)
        cout << "Element " << x << " is present at index " <<idx;
    else
        cout << "Element " << x << " is not present in the array";
    return 0;
}

// Code contributed by farzams101

C

/*
 * Approach : The idea is to compare x with the last element in arr[].
 * If an element is found at the last position, return it.
 * Else recur elmntSrch() for remaining array and element x.
 */

#include <stdio.h>

// Recursive function to search x in arr[]
int elmntSrch(int arr[], int size, int x) {
    int rec;

    size--;

    if (size >= 0) {
        if (arr[size] == x)
            return size;
        else
            rec = elmntSrch(arr, size, x);
    }
    else
        return -1;

    return rec;
}

int main(void) {
    int arr[] = {12, 34, 54, 2, 3};
    int size = sizeof(arr) / sizeof(arr[0]);
    int x = 3;
    int indx;

    indx = elmntSrch(arr, size, x);

    if (indx != -1)
        printf("Element %d is present at index %d", x, indx);
    else
        printf("Element %d is not present", x);

    return 0;
}

// This code is contributed by Manish Kumar (mkumar2789)

Java

// Recursive Java program to search x in array
class Test
{
     static int arr[] = {12, 34, 54, 2, 3};

     /* Recursive Method to search x in arr[l..r] */
     static int recSearch(int arr[], int l, int r, int x)
     {
          if (r < l)
             return -1;
          if (arr[l] == x)
             return l;
          if (arr[r] == x)
             return r;
          return recSearch(arr, l+1, r-1, x);
     }

     // Driver method
     public static void main(String[] args)
     {
        int x = 3;

        //Method call to find x
        int index = recSearch(arr, 0, arr.length-1, x);
        if (index != -1)
           System.out.println("Element " + x + " is present at index " +
                                                    index);
        else
            System.out.println("Element " + x + " is not present");
        }
 }

Python3

# Recursive function to search x in arr[l..r]
def recSearch( arr, l, r, x):
    if r < l:
        return -1
    if arr[l] == x:
        return l
    if arr[r] == x:
        return r
    return recSearch(arr, l+1, r-1, x)

# Driver Code
arr = [12, 34, 54, 2, 3]
n = len(arr)
x = 3
index = recSearch(arr, 0, n-1, x)
if index != -1:
    print ("Element", x,"is present at index %d" %(index))
else:
    print ("Element %d is not present" %(x))

# Contributed By Harshit Agrawal

C#

// Recursive C# program to
// search x in array
using System;

static class Test
{
    static int []arr = {12, 34, 54, 2, 3};

    /* Recursive Method to search x in arr[l..r] */
    static int recSearch(int []arr, int l, int r, int x)
    {
        if (r < l)
            return -1;
        if (arr[l] == x)
            return l;
        if (arr[r] == x)
            return r;
        return recSearch(arr, l+1, r-1, x);
    }

    // Driver method
    public static void Main(String[] args)
    {
        int x = 3;

        // Method call to find x
        int index = recSearch(arr, 0, arr.Length-1, x);

        if (index != -1)
        Console.Write("Element " + x +
                      " is present at index " + index);
        else
            Console.Write("Element " + x +
                          " is not present");
        }
}

// This code is contributed by Smitha Dinesh Semwal

PHP

<?php
// Recursive PHP program to
// search x in array

// Recursive function to
// search x in arr[l..r]
function recSearch($arr, int $l,
                   int $r, int $x)
{
    if ($r < $l)
        return -1;
    if ($arr[$l] == $x)
        return $l;
    if ($arr[$r] == $x)
        return $r;
     return recSearch($arr, $l+1, $r-1, $x);
}

    // Driver Code
    $arr = array(12, 34, 54, 2, 3); $i;
    $n = count($arr);
    $x = 3;
    $index = recSearch($arr, 0, $n - 1, $x);
    if ($index != -1)
    echo "Element"," ", $x," ",
         "is present at index ", $index;
    else
        echo "Element is not present", $x;

// This code is contributed by anuj_67.
?>

Javascript

<script>
// Recursive Javascript program to
// search x in array

// Recursive function to
// search x in arr[l..r]
function recSearch(arr, l, r, x)
{
    if (r < l)
        return -1;
    if (arr[l] == x)
        return l;
    if (arr[r] == x)
        return r;
     return recSearch(arr, l+1, r-1, x);
}

    // Driver Code
    let arr = [12, 34, 54, 2, 3];
    let i;
    let n = arr.length;
    let x = 23;
    let index = recSearch(arr, 0, n - 1, x);

    if (index != -1){
      document.write(`Element ${x} is present at index ${index}`);
    }
    else{
        document.write("Element is not present " + x);
    }

// This code is contributed by _saurabh_jaiswal.
</script>

Output

Element 11 is present at index 2

Explanation: We iterate through the array from the end by decrementing the size variable and recursively calling the function searchElement(). If the size variable becomes less than zero it means the element is not present in the array and we return -1. If a match is found, we return the size variable which is the index of the found element. This process is repeated until a value is returned to main().

It is important to note that if there are duplicate elements in the array, the index of the last matched element will be returned since we are (recursively) iterating the array from the end.

Time Complexity: O(N), where N is the size of the given array.
Auxiliary Space: O(N), For recursive call stack.

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