题解 | #第k轻的牛牛#

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @param k int整型 
     * @return int整型
     */
    int kthLighest(TreeNode* root, int k) {
        // write code here
        priority_queue<int, vector<int>, less<int>> q;
        queue<TreeNode*> que;
        que.push(root);
        while (que.size()) {
            int size = que.size();
            for (int i = 0; i < size; i++) {
                TreeNode* t = que.front();
                que.pop();
                if (q.size() < k) {
                    q.push(t->val);
                } else if (t->val < q.top()) {
                    q.pop();
                    q.push(t->val);
                }
                if (t->left) que.push(t->left);
                if (t->right) que.push(t->right);
            }
        }
        return q.top();
    }
};