正文
【树】Lowest Common Ancestor of a Binary Tree（递归）
小程序：扫一扫查出行【扫一扫了解最新限行尾号】
复制小程序
题目：
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.
思路：
节点a与节点b的公共祖先c一定满足：a与b分别出现在c的左右子树上；或者a,b一方是祖先元素。
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @param {TreeNode} p
* @param {TreeNode} q
* @return {TreeNode}
*/
var lowestCommonAncestor = function(root, p, q) {
if(root==null){
return;
}
if(root==p||root==q){
return root;
} var l=lowestCommonAncestor(root.left,p,q);
var r=lowestCommonAncestor(root.right,p,q); if(l&&r){
return root;
}else{
return l?l:r;
} };
