Time:O(h) Space:O(h) C++ struct T { TreeNode* lca; int depth; }; class Solution { public: TreeNode* lcaDeepestLeaves(TreeNode* root) { return dfs(root).lca; } private: T dfs(TreeNode* root) { if (!root) return {nullptr, 0}; T l = dfs(root->left); T r = dfs(root->right); if (l.depth > r.depth) return {l.lca, l.depth + 1}; if (l.depth < r.depth) return {r.lca, r.depth + 1}; return {root, l.depth + 1}; } }; JAVA class T { public TreeNode lca; public int depth; public T(TreeNode lca, int depth) { this.lca = lca; this.depth = depth; } }; class Solution { public TreeNode lcaDeepestLeaves(TreeNode root) { return dfs(root).lca; } private T dfs(TreeNode root) { if (root == null) return new T(null, 0); T l = dfs(root.left); T r = dfs(root.right); if (l.depth > r.depth) return new T(l.lca, l.depth + 1); if (l.depth < r.depth) return new T(r.lca, r.depth + 1); return new T(root, l.depth + 1); } }