Submission #7117767

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Source Code Expand

<?php
define('MOD', 10 ** 9 + 7);

fscanf(STDIN, '%d %d', $n, $k);
$a = array_map('intval', explode(' ', trim(fgets(STDIN))));

$cnt1 = $cnt2 = 0;
for ($i = 0; $i < $n; $i++) {
    for ($j = 0; $j < $n; $j++) {
        if ($i === $j) continue;

        if ($i < $j && $a[$i] > $a[$j]) $cnt1++;
        elseif ($i > $j && $a[$i] > $a[$j]) $cnt2++;
    }
}

$x1 = (1 + $k) * $k / 2 % MOD;
$x2 = (1 + $k - 1) * ($k - 1) / 2 % MOD;
$ans = (($cnt1 * $x1) % MOD + ($cnt2 * $x2) % MOD) % MOD;
echo $ans . PHP_EOL;

Submission Info

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