leetcode 235. 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.
还是bst树,bst树的左节点小于根节点小于右节点,依据此性质递归比较既可以找到公共父节点。注意输入的p,q有可能q->val > p->val或相反
/**
* 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 == nullptr || p == nullptr || q == nullptr) return nullptr;
if (max(q->val, p->val) < root->val) {
return lowestCommonAncestor(root->left, p, q);
} else if (min(p->val, q->val) > root->val) {
return lowestCommonAncestor(root->right, p, q);
} else {
return root;
}
}
};
原文地址:http://www.cnblogs.com/pk28/
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