LeetCode235——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.
实现:
void getAncestorVector(vector<TreeNode*>& vec, TreeNode* root, TreeNode* node) { if (root == NULL) return; vec.push_back(root); if (root->val == node->val) { return; } else if (root->val > node->val) { getAncestorVector(vec, root->left, node); } else if (root->val < node->val) { getAncestorVector(vec, root->right, node); } } TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) { vector<TreeNode*> pvecs; vector<TreeNode*> qvecs; getAncestorVector(pvecs, root, p); getAncestorVector(qvecs, root, q); int len = min(pvecs.size(), qvecs.size()); for (int i = 1; i < len; i++) { if (qvecs[i] == pvecs[i]) { continue; } return pvecs[i-1]; } return pvecs[len-1]; }