【LeetCode 236】Lowest Common Ancestor of a Binary Tree

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       /                  ___5__          ___1__
   /      \        /         6      _2       0       8
         /           7   4

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 private:
12     vector<TreeNode* > plist;
13     
14 public:
15     void rec(TreeNode *root, TreeNode *tar, vector<TreeNode* >& res)
16     {
17         if(root == tar)
18         {
19             vector<TreeNode* >::iterator it = plist.begin();
20             for(; it != plist.end(); it++)
21                 res.push_back(*it);
22             
23             return ;
24         }
25         
26         if(root->left != 0)
27         {
28             plist.push_back(root->left);
29             rec(root->left, tar, res);
30             plist.pop_back();
31         }
32         
33         if(root->right != 0)
34         {
35             plist.push_back(root->right);
36             rec(root->right, tar, res);
37             plist.pop_back();
38         }
39     }
40 
41     TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
42         if(root == 0)
43             return 0;
44         
45         vector<TreeNode* > list1, list2;
46         
47         plist.push_back(root);
48         rec(root, p, list1);
49         
50         plist.clear();
51         plist.push_back(root);
52         rec(root, q, list2);
53         
54         TreeNode  *ret = 0;
55         vector<TreeNode* >::iterator it1 = list1.begin();
56         vector<TreeNode* >::iterator it2 = list2.begin();
57         for(; it1 != list1.end() && it2 != list2.end(); it1++, it2++)
58         {
59             if(*it1 == *it2)
60                 ret = *it1;
61         }
62         
63         return ret;
64     }
65 };