private void DFS(TreeNode node, BinaryHeap <int> minHeap)
{
if (node == null)
{
return;
}
// SS: pre-order
minHeap.Push(node.val);
TestContext.Progress.WriteLine(node.val);
DFS(node.left, minHeap);
DFS(node.right, minHeap);
}
public int KthSmallest1(TreeNode root, int k)
{
var minHeap = BinaryHeap <int> .CreateHeap((p1, p2) => p1 > p2);
// SS: O(n * log n)
// n vertices, each pushed into min heap at log n each
DFS(root, minHeap);
// SS: O(k log n)
var value = -1;
var n = 0;
while (n < k)
{
value = minHeap.Pop();
n++;
}
// SS: total O(n log n)
// SS: O(log n) stack space and O(n) minheap
return(value);
}