Description

Submission

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    unordered_set<TreeNode*> nodes;
    TreeNode* ret = nullptr;

    int heightOfTree(TreeNode* root) { 
        if(!root) return -1;
        return max(heightOfTree(root->left), heightOfTree(root->right)) + 1;
    }

    void findDeepestLeaves(TreeNode* root, int height) {
        if(!root) return;
        if(height == 0) nodes.insert(root);
        else {
            findDeepestLeaves(root->left, height - 1);
            findDeepestLeaves(root->right, height - 1);
        }
    } 

    int dfs(TreeNode* root) {
        if(!root) return 0;
        int count = dfs(root->left) + dfs(root->right) + (nodes.find(root) != nodes.end());
        if(count == nodes.size() && !ret) {
            ret = root;
        }
        return count;
    }
public:
    TreeNode* lcaDeepestLeaves(TreeNode* root) {
        int height = heightOfTree(root);

        findDeepestLeaves(root, height);

        dfs(root);
        return ret;
    }
};