1123

/**
 * 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 {
    TreeNode *lca;
    int maxDepth = 0;
public:
    TreeNode* lcaDeepestLeaves(TreeNode* root) {
        dfs(root, 0);
        return lca;
    }

    int dfs(TreeNode *node, int depth){
        if(!node) return depth;
        int ldepth = dfs(node->left, depth+1);
        int rdepth = dfs(node->right, depth+1);
        maxDepth = max(maxDepth, max(ldepth, rdepth));
        if(ldepth == rdepth && ldepth == maxDepth)
            lca = node;
        return max(ldepth, rdepth);
    }
};