Lowest Common Ancestor of a Binary Search Tree

Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.

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).”

    _______6______   /              \___2__          ___8__

/ \ / \
0 _4 7 9
/ \
3 5
For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2 and 4 is 2, 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){            return NULL;        }        vector<TreeNode*> v1;        vector<TreeNode*> v2;        find(root,p,v1);//找p的前缀路径        find(root,q,v2);//找q的前缀路径        int len=min(v1.size(),v2.size());        TreeNode* last=NULL;        for(int i=0;i<len;i++){            if(v1[i]==v2[i]){                last=v1[i];            }else{                break;            }        }        return last;    }    void find(TreeNode* root, TreeNode* p, vector<TreeNode*> &v){        if(root==NULL){            return;        }        if(root==p){            v.push_back(root);            return;        }        v.push_back(root);        find(root->left,p,v);        if(v[v.size()-1]==p)//左子树中,找到了p的前缀路径            return;        v.pop_back();        v.push_back(root);        find(root->right,p,v);        if(v[v.size()-1]==p)//右子树中,找到了p的前缀路径            return;        v.pop_back();    }};