Algorithms: Range Queries

    static int fenwick_build(ReadOnlySpan<int> a, Span<int> tree) {
        checked {
            int n = a.Length;
            alg_require(((n >= 0) && (n <= 1000000)));
            alg_require((a.Length == n));
            alg_require((tree.Length == (n + 1)));
            int i = 0;
            int parent = 0;
            while ((i <= n)) {
                tree[i] = 0;
                i = (i + 1);
            }

function fenwick_build(array $a, array &$tree): int {
    alg_require(array_is_list($a));
    alg_require(array_is_list($tree));
    $n = count($a);
    alg_require((($n >= 0) && ($n <= 1000000)));
    alg_require((count($a) == $n));
    alg_require((count($tree) == alg_add($n, 1)));
    $i = 0;
    $parent = 0;
    while (($i <= $n)) {
        $tree[$i] = 0;
        $i = alg_add($i, 1);