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.
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
if(root==NULL||p==NULL||q==NULL)
return NULL;
return FindLCA(root,p,q);
} private:
TreeNode* FindLCA(TreeNode* root, TreeNode* p, TreeNode* q){
if(root==NULL)
return NULL;
if(root==p||root==q)
return root;
TreeNode* left;
TreeNode* right;
left=FindLCA(root->left,p,q);
right=FindLCA(root->right,p,q);
if(left&&right)
return root;
return left?left:right;
} };