给定一棵二叉搜索树，请找出其中第 k 大的节点的值。
示例 1:
输入: root = [3,1,4,null,2], k = 1
3
/ \
1 4
\
2
输出: 4示例 2:
输入: root = [5,3,6,2,4,null,null,1], k = 3
5
/ \
3 6
/ \
2 4
/
1
输出: 4限制：
- 1 ≤ k ≤ 二叉搜索树元素个数
//leetcode submit region begin(Prohibit modification and deletion)
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int kthLargest(TreeNode root, int k) {
Map<TreeNode, Integer> numMap = new HashMap<>();
int allNum = createNumMap(numMap, root);
return getKth(numMap, root, allNum + 1 - k);
}
private int getKth(Map<TreeNode, Integer> numMap, TreeNode node, int k) {
if (k < 1) {
return -1;
}
int leftNum = node.left == null ? 0 : numMap.get(node.left);
if (leftNum >= k) {
return getKth(numMap, node.left, k);
} else if (leftNum + 1 == k) {
return node.val;
} else {
return getKth(numMap, node.right, k - leftNum - 1);
}
}
private int createNumMap(Map<TreeNode, Integer> numMap, TreeNode node) {
if (node == null) {
return 0;
}
if (numMap.containsKey(node)) {
return numMap.get(node);
}
int leftNum = createNumMap(numMap, node.left);
int rightNum = createNumMap(numMap, node.right);
numMap.put(node, leftNum + rightNum + 1);
return leftNum + rightNum + 1;
}
}
//leetcode submit region end(Prohibit modification and deletion)
