Question

How to check if an array is monotonic in PHP

Answer 1

// check adjacent array elements to determine if the array is monotone increasing (or decreasing)

function isMonotonic($array) {
    $increase = 0;
    $decrease = 0;
    
    $size = count($array);
    
    for ($i = 0; $i < $size - 1; $i++) {
        if ($array[$i] > $array[$i + 1]) {
            $increase = 1;
        }
        if ($array[$i] < $array[$i + 1]) {
            $decrease = 1;
        }
        if ($increase == 1 && $decrease == 1) {
            return false;
        }
    }
    
    return true;
}
        
$array = array(1, 3, 4, 6, 8, 9, 11, 17, 18);

echo isMonotonic($array) ? "true" : "false";



/*
run:

true

*/

 

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