public SegmentTreeNode(int start, int end)
{
this.start = start;
this.end = end;
this.left = null;
this.right = null;
this.sum = 0;
}
private void Update(SegmentTreeNode node, int index, int val)
{
if (node.start == node.end)
{
node.sum = val;
}
else
{
int mid = (node.start + node.end) / 2;
if (index <= mid)
{
Update(node.left, index, val);
}
else
{
Update(node.right, index, val);
}
node.sum = node.left.sum + node.right.sum;
}
}
private int SumRange(SegmentTreeNode node, int start, int end)
{
if (node.end == end && node.start == start)
{
return(node.sum);
}
else
{
int mid = (node.start + node.end) / 2;
if (end <= mid)
{
return(SumRange(node.left, start, end));
}
else if (start >= mid + 1)
{
return(SumRange(node.right, start, end));
}
else
{
return(SumRange(node.right, mid + 1, end) + SumRange(node.left, start, mid));
}
}
}
private SegmentTreeNode BuildSegmentTree(int[] nums, int start, int end)
{
if (start > end)
{
return(null);
}
else
{
SegmentTreeNode res = new SegmentTreeNode(start, end);
if (start == end)
{
res.sum = nums[start];
}
else
{
int mid = (start + end) / 2;
res.left = BuildSegmentTree(nums, start, mid);
res.right = BuildSegmentTree(nums, mid + 1, end);
res.sum = res.left.sum + res.right.sum;
}
return(res);
}
}
public NumArray(int[] nums)
{
root = BuildSegmentTree(nums, 0, nums.Length - 1);
}
