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];
    }