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LowestCommonAncestorOfABinarySearchTree.cpp
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LowestCommonAncestorOfABinarySearchTree.cpp
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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 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.
**********************************/
/**
* 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) {
while (true) {
if (p->val > root->val) {
if (q->val > root->val) {
root = root->right;
} else {
return (q->val < root->val) ? root : q;
}
} else if (p->val < root->val) {
if (q->val < root->val) {
root = root->left;
} else {
return (q->val > root->val) ? root : q;
}
} else {
return p;
}
}
}
};