标签:Lowest 1644 right TreeNode Binary return null root left
When we get this problem, we need to confirm the following 2 questions:
1. Can root, p or q be null? (No)
2. Are both p and q in the tree (No, either p or q mignt not in the tree), this is the only difference with 236. Lowest Common Ancestor of a Binary Tree
3. Can p be equal to q? (No)
boolean meetp, meetq; public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { TreeNode node = helper(root, p, q); if(meetp&&meetq) return node; else return null; } private TreeNode helper(TreeNode root, TreeNode p, TreeNode q){ if(root==null) return null; if(root==p) meetp = true; if(root==q) meetq = true; TreeNode left = helper(root.left, p,q); TreeNode right = helper(root.right, p, q); if(left!=null&&right!=null||root==p||root== q) //since we need to traverse the whole tree, "root==p||root==q" is moved to here return root; if(left==null) return right; else return left; }
标签:Lowest,1644,right,TreeNode,Binary,return,null,root,left 来源: https://www.cnblogs.com/feiflytech/p/15869995.html
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