Recursion and Stack memory

When I was thinking about the problem Validate Binary Search Tree, my code runs like this: 12345678910111213141516171819public boolean isValidBST(TreeNode root) { TreeNode previous = null;

Corner cases for binary trees

When doing LeetCode problems, some corner cases should be considered when traversing through the tree, otherwise unexpected errors shall appear. Examples:Symmetric TreeSame Tree The following code tak

DFS in Binary Tree

Let’s think about this problem: Sum Root to Leaf Numbers. A general solution is like below:123456789101112131415161718192021222324252627282930313233public int sumNumbers(TreeNode root) { if (