Today I have done leetcode's January LeetCoding Challenge with cpp.

January LeetCoding Challenge 9

Description

Smallest Subtree with all the Deepest Nodes

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.

Constraints:

• The number of nodes in the tree will be in the range [1, 500].
• 0 <= Node.val <= 500
• The values of the nodes in the tree are unique.

Note: This question is the same as 1123: https://leetcode.com/problems/lowest-common-ancestor-of-deepest-leaves/

Solution

class Solution {
  pair<TreeNode*, int> helper(TreeNode* root, int level) {
    if(!root) return make_pair(root, 0);
    auto left = helper(root->left, level+1);
    auto right = helper(root->right, level+1);
    if(left.second == right.second) return make_pair(root, left.second ? left.second : level);
    if(left.second < right.second) return right;
    return left;
  }
public:
  TreeNode* subtreeWithAllDeepest(TreeNode* root) {
    return helper(root, 0).first;
  }
};

// Accepted
// 58/58 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 27.2 % of cpp submissions (16.3 MB)