[LeetCode]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.

［思路］根据二叉树的特点，最小的公共祖先就是在两个点值之间的根节点。特别要注意p，q两个点的大小是不确定的。

/** * 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) {        int min = p->val>q->val?q->val:p->val;        int max = p->val>q->val?p->val:q->val;        while(true){            if(root->val>=min&&root->val<=max)                break;            if(root->val<min){                root = root->right;            }            if(root->val>max){                root = root->left;            }        }        return root;    }};