Leetcode•Jun 03, 2025
Smallest Subtree with all the Deepest Nodes
Hazrat Ali
Leetcode
Given the root of a binary tree, the depth of each node is the shortest distance to the root.
Return the smallest subtree such that it contains all the deepest nodes in the original tree.
A node is called the deepest if it has the largest depth possible among any node in the entire tree.
The subtree of a node is a tree consisting of that node, plus the set of all descendants of that node.
Example 1:
Input: root = [3,5,1,6,2,0,8,null,null,7,4] Output: [2,7,4] Explanation: We return the node with value 2, colored in yellow in the diagram. The nodes coloured in blue are the deepest nodes of the tree. Notice that nodes 5, 3 and 2 contain the deepest nodes in the tree but node 2 is the smallest subtree among them, so we return it.
Example 2:
Input: root = [1] Output: [1] Explanation: The root is the deepest node in the tree.
Example 3:
Input: root = [0,1,3,null,2] Output: [2] Explanation: The deepest node in the tree is 2, the valid subtrees are the subtrees of nodes 2, 1 and 0 but the subtree of node 2 is the smallest.
Solution
/**
* @param {TreeNode} root
* @return {TreeNode}
*/
const subtreeWithAllDeepest = root => {
return helper(root).node;
};
const helper = root => {
if (!root) {
return { node: null, dist: 0 };
}
const left = helper(root.left);
const right = helper(root.right);
if (left.dist > right.dist) {
return { node: left.node, dist: left.dist + 1 };
}
if (left.dist < right.dist) {
return { node: right.node, dist: right.dist + 1 };
}
return { node: root, dist: left.dist + 1 };
};