st_create

struct Node
{
	int val;
	int mark;

	Node() : val(0), mark(0)
	{

	}
};

SegmentTree(vector<int> nums) {
	n = nums.size();
	if (!n)return;
	st = vector<Node>(3 * n);
	createTree(nums, 0, n - 1, 0);
}

void createTree(vector<int>& nums, int lo, int hi, int i)
{
	if (lo == hi)
	{
		st[i].val = nums[lo];
		return;
	}
	int mid = lo + (hi - lo) / 2;
	createTree(nums, lo, mid, 2 * i + 1);
	createTree(nums, mid + 1, hi, 2 * i + 2);
	st[i].val = st[2 * i + 1].val + st[2 * i + 2].val;
}