leetcode 235. Lowest Common Ancestor of a Binary Search Tree

原题：

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.

找到二叉排序树的最近的共同根。

其实只要root->val的值在q，p的值的闭区间就可以了。

代码如下：

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     struct TreeNode *left; *     struct TreeNode *right; * }; */struct TreeNode* lowestCommonAncestor(struct TreeNode* root, struct TreeNode* p, struct TreeNode* q) {    if(p->val<q->val)    {        struct TreeNode* temp;        temp=p;        p=q;        q=temp;    }    if(root!=NULL&&root->val>p->val)    {        return lowestCommonAncestor(root->left,p,q);    }    if(root!=NULL&&root->val<q->val)    {        return lowestCommonAncestor(root->right,p,q);    }    printf("%d,%d",p->val,q->val);    return root; }

简单的递归。