标签：out tco tput image win where null rip lca
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 p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).”
Given the following binary search tree: root = [3,5,1,6,2,0,8,null,null,7,4]
_______3______ / ___5__ ___1__ / \ / 6 _2 0 8 / 7 4
Example 1:
Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1 Output: 3 Explanation: The LCA of of nodes 5 and 1 is 3.
Example 2:
Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4 Output: 5 Explanation: The LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.
题意：
二叉树最近公共祖先
思路：
用自底向上(bottom-up)的思路，先看看是否能在root的左子树中找到p或q，再看看能否在右子树中找到，
p和q都在右子树p和q都在左子树
代码：
1 class Solution { 2 public TreeNode lowestCommonAncestor(TreeNode root, TreeNode node1, TreeNode node2) { 3 if (root == null || root == node1 || root == node2) { 4 return root; 5 } 6 7 // Divide 8 TreeNode left = lowestCommonAncestor(root.left, node1, node2); 9 TreeNode right = lowestCommonAncestor(root.right, node1, node2); 10 11 // Conquer 12 if (left != null && right != null) { 13 return root; 14 } 15 if (left != null) { 16 return left; 17 } 18 if (right != null) { 19 return right; 20 } 21 return null; 22 } 23 }
[leetcode]236. Lowest Common Ancestor of a Binary Tree二叉树最近公共祖先
标签：out tco tput image win where null rip lca
原文地址：https://www.cnblogs.com/liuliu5151/p/9158486.html
