标签:lowest common ancestor bst 二叉树
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();
}
};
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Lowest Common Ancestor of a Binary Search Tree
标签:lowest common ancestor bst 二叉树
原文地址:http://blog.csdn.net/u010786672/article/details/46844747