LeetCode OJ 236. Lowest Common Ancestor of a Binary Tree
Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.
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).”
_______3______ / \ ___5__ ___1__ / \ / \ 6 _2 0 8 / \ 7 4
For example, the lowest common ancestor (LCA) of nodes 5
and 1
is 3
. Another example is LCA of nodes 5
and 4
is 5
, since a node can be a descendant of itself according to the LCA definition.
这个题目一开始很是困惑~不知道该如何下手。发现别人的解答很是简单,发现递归真是一门学问啊!
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */ 10 public class Solution { 11 public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { 12 if(root == null) return null; 13 if(root == p || root == q) return root; 14 TreeNode left = lowestCommonAncestor(root.left, p, q); 15 TreeNode right = lowestCommonAncestor(root.right, p, q); 16 return left != null && right != null ? root : left == null ? right : left; 17 } 18 19 }