Question

How to find the equilibrium index of an array (sum arr[0 to index - 1] == sum arr[index + 1 to size]) in PHP

Answer 1

function getEquilibriumIndex($arr) {
    $sum_arr = 0;
    $left_part_sum = 0;
    $size = count($arr);
    
    for ($i = 0; $i < $size; $i++) {
        $sum_arr += $arr[$i];
    }
    
    for ($i = 0; $i < $size; $i++) {
        $sum_arr -= $arr[$i];
        if ($left_part_sum == $sum_arr) {
            return $i;
        }
        $left_part_sum += $arr[$i];
    }
    return -1;
}

        
$arr = array(-9, 2, 5, 8, -7, 4, 1);
        
echo "equilibrium index = " . getEquilibriumIndex($arr);




/*
run:

equilibrium index = 3

*/

 

70+ SQL courses for beginners and professionals