Solution2.cpp

/**
 * 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 {
public:
    TreeNode* findNearestRightNode(TreeNode* root, TreeNode* u) {
        TreeNode* ans;
        int d = 0;
        function<void(TreeNode*, int)> dfs = [&](TreeNode* root, int i) {
            if (!root || ans) {
                return;
            }
            if (d == i) {
                ans = root;
                return;
            }
            if (root == u) {
                d = i;
                return;
            }
            dfs(root->left, i + 1);
            dfs(root->right, i + 1);
        };
        dfs(root, 1);
        return ans;
    }
};