LeetCode 235. Lowest Common Ancestor of a Binary Search Tree (二叉搜索树最近的共同祖先)
Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.
According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”
_______6______
/ \
___2__ ___8__
/ \ / \
0 _4 7 9
/ \
3 5
For example, the lowest common ancestor (LCA) of nodes 2
and 8
is 6
. Another example is LCA of nodes 2
and 4
is 2
, since a node can be a descendant of itself according to the LCA definition.
Java Solution:
Runtime beats 62.62%
完成日期:07/04/2017
关键词:Tree (BST); LCA (lowest common ancestor)
关键点:只遍历左边或者右边根据BST的特性
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution
{ public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q)
{
if(root == null)
return null; // go into left child if the greater from p and q is smaller than root;
if(Math.max(p.val, q.val) < root.val)
return lowestCommonAncestor(root.left, p, q); // go into right child if the smaller from p and q is greater than root;
if(Math.min(p.val, q.val) > root.val)
return lowestCommonAncestor(root.right, p, q); // if p and q are not at the left side, and also not at the right side
// meaning p and q are at the both side or root is p or q , another one is at one side.
return root;
} }
参考资料:
http://www.cnblogs.com/grandyang/p/4640572.html
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