【LeetCode】235. Lowest Common Ancestor of a Binary Search Tree

LeetCode-235

Links:https://leetcode.com/problems/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

_______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.

题意：找到最近共同祖先节点

思路：根据BST的特性，如果pq的值都大于root，到right子树查找，如果都小于，到left子树查询，否则返回root…

/**
 * 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->val > p->val && root->val>q->val)
        {
            return lowestCommonAncestor(root->left, p, q);
        }
        else if(root->val < p->val && root->val<q->val)
        {
            return lowestCommonAncestor(root->right, p, q);
        }
        else{
            return root;
        }
    }
};

/**

* 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->val > p->val && root->val>q->val)

{

return lowestCommonAncestor(root->left, p, q);

}

else if(root->val < p->val && root->val<q->val)

{

return lowestCommonAncestor(root->right, p, q);

}

else{

return root;

}

};

【LeetCode】235. Lowest Common Ancestor of a Binary Search Tree

Tagged on: LeetCode