Solution.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:
    queue<int> q;
    double target;
    int k;

    vector<int> closestKValues(TreeNode* root, double target, int k) {
        this->target = target;
        this->k = k;
        dfs(root);
        vector<int> ans;
        while (!q.empty()) {
            ans.push_back(q.front());
            q.pop();
        }
        return ans;
    }

    void dfs(TreeNode* root) {
        if (!root) return;
        dfs(root->left);
        if (q.size() < k)
            q.push(root->val);
        else {
            if (abs(root->val - target) >= abs(q.front() - target)) return;
            q.pop();
            q.push(root->val);
        }
        dfs(root->right);
    }
};