LeetCode 235: Lowest Common Ancestor of a Binary Search Tree
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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 allowa 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.
分析:
在二叉查找树种,寻找两个节点的最低公共祖先。
1、如果a、b都比根节点小,则在左子树中递归查找公共节点。
2、如果a、b都比根节点大,则在右子树中查找公共祖先节点。
3、如果a、b一个比根节点大,一个比根节点小,或者有一个等于根节点,则根节点即为最低公共祖先。
class Solution {public: TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) { if (root == NULL) { return NULL; } int min = (p->val > q->val ? q->val:p->val); int max = (p->val > q->val ? p->val: q->val); if(max < root->val) return lowestCommonAncestor(root->left, p, q); if (min > root->val) { return lowestCommonAncestor(root->right, p, q); } return root; }};
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