Write a program to get second highest number in an array using PHP ?

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Given an array of integers and the task is to write a program that efficiently finds the second-largest element present in the array.

Example:

Input: arr[] = {13, 14, 15, 16, 17, 18}
Output: The second largest element is 17.
Explanation: The largest element of the array
is 35 and the second largest element is 17

Input: arr[] = {10, 5, 10}
Output: The second largest element is 5.
Explanation: The largest element of the array
is 10 and the second largest element is 5

Input: arr[] = {10, 10, 10}
Output: The second largest does not exist.
Explanation: Largest element of the array  
is 10 there is no second largest element

Simple Solution:

Approach: The idea is to sort the array in descending order and then return the second element which is not equal to the largest element from the sorted array.

PHP

<?php
function bubbleSort(&$arr) {
    $n = sizeof($arr);
 
    // Traverse through all array elements
    for($i = 0; $i < $n; $i++) {
        $swapped = False;
 
        // Last i elements are already
        // in place
        for ($j = 0; $j < $n - $i - 1; $j++) {
             
            // traverse the array from 0 to
            // n-i-1. Swap if the element
            // found is greater than the
            // next element
            if ($arr[$j] <$arr[$j+1]) {
                $t = $arr[$j];
                $arr[$j] = $arr[$j+1];
                $arr[$j+1] = $t;
                $swapped = True;
            }
        }
 
        // IF no two elements were swapped
        // by inner loop, then break
        if ($swapped == False)
            break;
    }
}
         
// Driver code to test above
$arr = array(64, 34, 25, 12, 22, 11, 90);
$len = sizeof($arr);
bubbleSort($arr);
 
if($arr[0] == $arr[1]) {
  echo "No element";
}
else {
  echo "Second Largest element is ".$arr[1];
}
     
?>

Output

Second Largest element is 64

Complexity Analysis:

Worst and Average Case Time Complexity: O(n*n). Worst case occurs when array is reverse sorted.
Best Case Time Complexity: O(n). Best case occurs when array is already sorted.
Auxiliary Space: O(1)

Boundary Cases: Bubble sort takes minimum time (Order of n) when elements are already sorted.
Sorting In Place: Yes
Stable: Yes

Another Approach: Find the second largest element in a single traversal.

Below is the complete algorithm for doing this:

1) Initialize the first as 0 (i.e, index of arr[0] element)
2) Start traversing the array from array[1],
  a) If the current element in array say arr[i] is greater
     than first. Then update first and second as,
     second = first
     first = arr[i]
  b) If the current element is in between first and second,
     then update second to store the value of current variable as
     second = arr[i]
3) Return the value stored in second.

PHP

<?php
   
// PHP program to find second largest
// element in an array
 
// Function to print the
// second largest elements
function print2largest($arr, $arr_size) {
 
    // There should be atleast
    // two elements
    if ($arr_size < 2) {
        echo(" Invalid Input ");
        return;
    }
 
    $first = $second = PHP_INT_MIN;
   
    for ($i = 0; $i < $arr_size ; $i++) {
         
        // If current element is
        // smaller than first
        // then update both
        // first and second
        if ($arr[$i] > $first) {
            $second = $first;
            $first = $arr[$i];
        }
 
        // If arr[i] is in
        // between first and
        // second then update
        // second
        else if ($arr[$i] > $second &&
                $arr[$i] != $first)
            $second = $arr[$i];
    }
    if ($second == PHP_INT_MIN)
        echo("There is no second largest element\n");
    else
        echo("The second largest element is "
                 . $second . "\n");
}
 
// Driver Code
$arr = array(12, 35, 1, 10, 34, 1);
$n = sizeof($arr);
print2largest($arr, $n);
 
?>

Output:

The second largest element is 34

Another Approach: Sort the array in descending order using the PHP rsort() method and then return the second element from the sorted array. Here, we have declared a returnSecondHighest() method that accepts an array. By implementing the rsort() method in PHP that will sort the array in descending order. Now, store the second-highest element of the sorted array by using the 1st index of the array in a variable. Here, we declare the user-defined array of numbers & call the returnSecondHighest() method and print the second-highest element of the array.

PHP Code:

PHP

<?php
     
    function returnSecondHighest(array $myarray){
    
        // Sort the array in descending order
        rsort($myarray);
    
        // Save the element from the second last position of sorted array
        $secondHighest = $myarray[1];
    
        // Return second highest number
        return $secondHighest;
    }
 
    // Driver code to test above
    $arr = array(64, 34, 25, 12, 22, 11, 90);
 
    // Call the function and print output
    echo "Second highest number : ".returnSecondHighest($arr);
?>

Output: The time complexity of this program is O(nlogn) as the PHP rsort() method takes O(nlogn) where n is the number of elements in the array parameter.