Question

How to count the triangles that can be formed using three different elements of an array in PHP

Answer 1

function GetNumberOfTriangles($arr) {
    $size = count($arr);
    $count = 0;
    
    for ($i = 0; $i < $size; $i++) {
        for ($j = $i + 1; $j < $size; $j++) {
            for ($k = $j + 1; $k < $size; $k++) {
                // triangle = sum of two sides > value of the third side
                if ($arr[$i] + $arr[$j] > $arr[$k] && 
                    $arr[$i] + $arr[$k] > $arr[$j] && 
                    $arr[$k] + $arr[$j] > $arr[$i]) {
                    echo $arr[$i] . " " . $arr[$j] . " " . $arr[$k] . "\n";
                    $count++;
                }
            }
        }
    }
    
    return $count;
}
        
$arr = array(2, 3, 4, 5, 6, 7);
        
echo GetNumberOfTriangles($arr);




/*
run:

2 3 4
2 4 5
2 5 6
2 6 7
3 4 5
3 4 6
3 5 6
3 5 7
3 6 7
4 5 6
4 5 7
4 6 7
5 6 7
13

*/

 

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