您的位置:首页 > 其它

235. Lowest Common Ancestor of a Binary Search Tree

2016-03-24 23:15 399 查看
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.

题意:找到二叉搜索树两个结点的最近公共祖先节点。

思路:利用二叉搜索树的特点,如果root值在p值和q值之间,则root即为最近的公共祖先,否则根据root值与p值q值的关系向左子树找或向右子树找。

/**
* 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 == NULL)
return root;
int a, b;
if (p->val < q->val){
a = p->val;//a is little
b = q->val;
}
else{
a = q->val;
b = p->val;
}
int c = root->val;
if (c < a){
return lowestCommonAncestor(root->right, p, q);
}
else if (c == a)
return root;
else if (c > a){
if (c <= b)
return root;
else if (c > b)
return lowestCommonAncestor(root->left, p, q);
}
}
};
内容来自用户分享和网络整理,不保证内容的准确性,如有侵权内容,可联系管理员处理 点击这里给我发消息
标签: