private int FindSumRangeInTree(SumSegmentTreeNode tree, int start, int end)
{
if (tree == null)
{
return(-1);
}
if (tree.Start == start && tree.End == end)
{
return(tree.Sum);
}
var mid = tree.Start + (tree.End - tree.Start) / 2;
if (end <= mid)
{
return(FindSumRangeInTree(tree.Left, start, end));
}
if (start > mid)
{
return(FindSumRangeInTree(tree.Right, start, end));
}
// The range contains mid.
return(FindSumRangeInTree(tree.Right, mid + 1, end) + FindSumRangeInTree(tree.Left, start, mid));
}
private SumSegmentTreeNode BuildSegmentTree(int[] nums, int start, int end)
{
if (start > end)
{
return(null);
}
var treeNode = new SumSegmentTreeNode(start, end);
if (start == end)
{
treeNode.Sum = nums[start];
}
else
{
var mid = start + (end - start) / 2;
treeNode.Left = BuildSegmentTree(nums, start, mid);
treeNode.Right = BuildSegmentTree(nums, mid + 1, end);
treeNode.Sum = treeNode.Left.Sum + treeNode.Right.Sum;
}
return(treeNode);
}
private void UpdateTree(SumSegmentTreeNode tree, int pos, int val)
{
// Handle single node tree
if (tree.Start == tree.End)
{
tree.Sum = val;
}
else
{
var mid = tree.Start + (tree.End - tree.Start) / 2;
// Recursively update segment tree children.
if (pos <= mid)
{
UpdateTree(tree.Left, pos, val);
}
else
{
UpdateTree(tree.Right, pos, val);
}
tree.Sum = tree.Left.Sum + tree.Right.Sum;
}
}
public NumArrayWithSegmentTree(int[] nums)
{
_root = BuildSegmentTree(nums, 0, nums.Length);
}
