PHP Exercises: Check whether the sequence of numbers 1, 2, 3 appears in a given array of integers somewhere

Last update on May 28 2025 13:07:50 (UTC/GMT +8 hours)

34. Check for Sequence 1,2,3 in Array

Write a PHP program to check whether the sequence of numbers 1, 2, 3 appears in a given array of integers somewhere.

Sample Solution:

PHP Code :

<?php
// Define a function that checks if the sequence 1, 2, 3 appears in an array
function test($nums)
{
    // Iterate through the array to find the sequence
    for ($i = 0; $i < sizeof($nums)-2; $i++)
    {
        // Check if the current, next, and next-next elements form the sequence 1, 2, 3
        if ($nums[$i] == 1 && $nums[$i + 1] == 2 && $nums[$i + 2] == 3)
            return true;
    }
    
    // If the sequence is not found, return false
    return false;
}

// Test the function with different arrays
var_dump(test(array(1,1,2,3,1)));
var_dump(test(array(1,1,2,4,1)));
var_dump(test(array(1,1,2,1,2,3)));
?>

Explanation:

Function Definition:

The test function takes an array of numbers $nums as input and checks if the sequence [1, 2, 3] appears anywhere in the array.

Loop through Array:

The for loop iterates from the start of the array up to the third-to-last element to ensure there are enough elements left to check for the sequence.
sizeof($nums) - 2 ensures we don't go out of bounds when checking three consecutive elements.

Check for Sequence:

Inside the loop, the code checks if three consecutive elements form the sequence [1, 2, 3] by comparing:

$nums[$i] == 1
$nums[$i + 1] == 2
$nums[$i + 2] == 3
If the sequence is found, the function returns true.

Return False if Sequence Not Found:

If the loop completes without finding the sequence [1, 2, 3], the function returns false.

Output:

bool(true)
bool(false)
bool(true)

Visual Presentation:

PHP Basic Algorithm Exercises: Check whether the sequence of numbers 1, 2, 3 appears in a given array of integers somewhere.

Flowchart:

For more Practice: Solve these Related Problems:

Write a PHP script to check if the sequence 1, 2, 3 appears consecutively anywhere in an integer array.
Write a PHP function to scan an array for a specific sub-sequence and return a boolean result if found.
Write a PHP program to search for contiguous numbers matching the pattern 1, 2, 3 using a sliding window technique.
Write a PHP script to implement subarray matching logic to detect if the integer sequence 1,2,3 occurs in order.

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