題目描述

給定一顆二叉搜尋樹，請找出其中的第k大的結點。例如， 5 / \ 3 7 /\ /\ 2 4 6 8 中，按結點數值大小順序第三個結點的值為4。

實驗平臺：牛客網

解決思路：

java:

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;
    }
}
*/
public class Solution {
    int k = 0
 
;

    TreeNode KthNode(TreeNode pRoot, int k) {
        if (pRoot == null || k == 0) {
            return null;
        }
        this.k = k;
        return getKthNode(pRoot);
    }

    TreeNode getKthNode(TreeNode pRoot) {
        TreeNode target = null;
        if (pRoot.left != null) {
            target = getKthNode(pRoot.left
 
);
        }
        if (target == null) {
            if (k == 1) {
                target = pRoot;
            } else {
                k--;
            }
        }
        if (target == null && pRoot.right != null) {
            target = getKthNode(pRoot.right);
        }
        return target;
    }
}
 

python:

略