Question

How to check if a sequence of numbers is a Harmonic progression (reciprocals Arithmetic progression) in PHP

Answer 1

// a, b, c, d are HP if 1/a, 1/b, 1/c, 1/d are AP -> 1/a, 1/(a+diff), 1/(a+2*diff)...

function isHarmonicProgression($arr) {
    $size = count($arr);
    if ($size == 1) return 1;

    $difference = (1.0 / $arr[1]) - (1.0 / $arr[0]);

    for ($i = 2; $i < $size; $i++) {
        if ((1.0 / $arr[$i]) - (1.0 / $arr[$i - 1]) != $difference) {
            return 0; 
        }
    }

    return 1; 
}

$arr = [1.0 / 5, 1.0 / 10, 1.0 / 15, 1.0 / 20, 1.0 / 25]; 

echo isHarmonicProgression($arr) == 1 ? "Yes" : "No";




/*
run:
 
Yes
 
*/

 

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