Description
Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.
Solution
- 獲取左子樹的節點數number
如果左子樹節點數剛好爲k-1,說明該節點爲第k個,否則向左子樹找或者向右子樹找。
Code
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int kthSmallest(TreeNode root, int k) {
int number = number(root.left);
if (number == k - 1) {
// 如果左子樹節點數剛好爲k-1,說明該節點爲第k個
return root.val;
} else if (number >= k) {
// 第k個在左子樹
return kthSmallest(root.left, k);
} else {
// 第k個在右子樹
return kthSmallest(root.right, k - 1 - number);
}
}
// 獲取該節點的所有葉子數
public int number(TreeNode node) {
if (node == null) {
return 0;
} else {
return number(node.left) + number(node.right) + 1;
}
}
}