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Php Program for Last duplicate element in a sorted array

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  • Last Updated : 10 Jun, 2022
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We have a sorted array with duplicate elements and we have to find the index of last duplicate element and print index of it and also print the duplicate element. If no such element found print a message. 

Input : arr[] = {1, 5, 5, 6, 6, 7}
Output :
Last index: 4
Last duplicate item: 6

Input : arr[] = {1, 2, 3, 4, 5}
Output : No duplicate found


We simply iterate through the array in reverse order and compare the current and previous element. If a match is found then we print the index and duplicate element. As this is sorted array it will be the last duplicate. If no such element is found we will print the message for it.

1- for i = n-1 to 0
     if (arr[i] == arr[i-1])
        Print current element and its index.
2- If no such element found print a message 
   of no duplicate found.



// PHP program to print last
// duplicate element and its
// index in a sorted array
function dupLastIndex($arr, $n)
    // if array is null or size is less
    // than equal to 0 return
    if ($arr == null or $n <= 0)
    // compare elements and return last
    // duplicate and its index
    for ( $i = $n - 1; $i > 0; $i--)
        if ($arr[$i] == $arr[$i - 1])
            echo "Last index:", $i , "
            echo "Last duplicate item:", $arr[$i];
    // If we reach here, then
    // no duplicate found.
    echo "no duplicate found";
// Driver Code
$arr = array(1, 5, 5, 6, 6, 7, 9);
$n = count($arr);
dupLastIndex($arr, $n);
// This code is contributed by anuj_67.


Last index: 4
Last duplicate item: 6


Time Complexity: O(n), where n represents the size of the given array.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

Please refer complete article on Last duplicate element in a sorted array for more details!

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