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.

===============

CLA问题,

利用递归方式:采用的后序遍历的思想,LRN

左子树查找,右子树查找,这个思路进行.

TreeNode *seek(TreeNode *root,TreeNode *p,TreeNode *q){
help_seek();
}
void help_seek(TreeNode *root, TreeNode *p,TreeNode *q,bool l,bool r){
if(r && l) cout<<"find the value""<<root->val<<endl;
if(root){
help_seek(root->left);
help_seek(root->right);
}
}

???????

====

代码:

/**
* 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==nullptr) return NULL;
if(root==p || root==q) return root;
TreeNode *left_lca = lowestCommonAncestor(root->left,p,q);
TreeNode *right_lca = lowestCommonAncestor(root->right,p,q);
if(left_lca&&right_lca) return root; return left_lca==nullptr? right_lca:left_lca;
}
};

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