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 5For 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.A:
public class Solution { public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { if(p.val > q.val) return lowestCommonAncestor(root,q,p); return helper(root,p,q); } private TreeNode helper(TreeNode root, TreeNode p, TreeNode q) { if(root.val<p.val) return helper(root.right,p,q); else if(root.val > q.val) return helper(root.left,p,q); return root; } }
其实这道题,无关Binary Search Tree ---虽然利用起来,效率会高一些些
public class Solution { public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { if(root==null || root == p || root == q) return root; TreeNode left = lowestCommonAncestor(root.left,p,q); TreeNode right = lowestCommonAncestor(root.right, p, q); if(left == null) return right; if(right ==null) return left; return root; } }
Mistakes:
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