剑指 Offer 54. 二叉搜索树的第k大节点

思路

 

 

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    int cnt = 0;
public:
    int kthLargest(TreeNode* root, int k) {
        int res;
        inOrderTraverse(root, k, res);

        return res;
    }

    void inOrderTraverse(TreeNode *root, int k, int& res) {
        if(cnt == k || root == NULL)
            return;
        inOrderTraverse(root->right, k, res);
        cnt++;
        if(cnt == k) {
            res = root->val;
            return;
        }
        inOrderTraverse(root->left, k, res);
        
    }
};