Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.
“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.
Solution: 递归check
思路:
Time Complexity: O(N) Space Complexity: O(N) 递归缓存
Solution Code:
class Solution {
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
if(root == null) return null;
/* if necessary
if(p == null || q == null) {
if(p == null) return q;
else return p;
}
*/
if(p.val < root.val && q.val < root.val) {
return lowestCommonAncestor(root.left, p, q);
}
else if(p.val > root.val && q.val > root.val) {
return lowestCommonAncestor(root.right, p, q);
}
// this node is the LCA
else return root;
}
}