最近公共祖先 LCA 递归非递归

 1 /**
 2  * Definition of TreeNode:
 3  * class TreeNode {
 4  * public:
 5  *     int val;
 6  *     TreeNode *left, *right;
 7  *     TreeNode(int val) {
 8  *         this->val = val;
 9  *         this->left = this->right = NULL;
10  *     }
11  * }
12  */
13 
14 
15 class Solution {
16 public:
17     /*
18      * @param root: The root of the binary search tree.
19      * @param A: A TreeNode in a Binary.
20      * @param B: A TreeNode in a Binary.
21      * @return: Return the least common ancestor(LCA) of the two nodes.
22      */
23     TreeNode * lowestCommonAncestor(TreeNode * root, TreeNode * A, TreeNode * B) {
24         // write your code here
25         //如果当前节点为空，或者与目标节点中的一个相同，则返回该节点
26         if(root == NULL)    return NULL;
27         if(root==A || root==B)  return root;
28         
29         //递归寻找A B在左右子树的位置
30         TreeNode* left = lowestCommonAncestor(root->left,A,B);
31         TreeNode* right = lowestCommonAncestor(root->right,A,B);
32         
33         //如果A B分别位于root的两侧，则root是他们的LCA，否则是左子树或者右子树
34         if(left&&right) return root;
35         
36         return left?left:right;
37         
38         
39     }
40 };