面试题54. 二叉搜索树的第k大节点

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    int res,k;
    public int kthLargest(TreeNode root, int k) {
        this.k = k;
        dfs(root);
        return res;
    }

    void dfs(TreeNode root)
    {
        if(root == null)
        {
            return;
        }
//根正苗红的倒中序，，左中右，变成，右中左
        dfs(root.right);
        if(k == 0) return;
        k = k - 1;
        if(k == 0) res = root.val;
        dfs(root.left);
    }
}