Lowest Common Ancestor of a Binary Tree

普通二叉樹尋找公共祖先，二叉樹的問題基本就是遍歷，最小的公共祖先的知足下面一個性質：一、兩個節點分別在左右子樹上，二、一個節點是另外一節點的祖先

 1 class Solution {
 2 public:
 3     TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
 4         TreeNode* pr,*qr;
 5         if(root==NULL)
 6             return NULL;
 7         cout<<root->val<<endl;
 8         if(p==root||q==root)
 9             return root;
10         pr=lowestCommonAncestor(root->left,p,q);
11         qr=lowestCommonAncestor(root->right,p,q);
12         if(pr!=NULL&&qr!=NULL)
13            return root;
14         if(pr!=NULL)
15             return pr;
16         else
17             return qr;
18     }
19 };