参考 https://leetcode.com/discuss/interview-question/358676/Google-or-Remove-Extra-Edge
Given a binary tree, where an arbitary node has 2 parents i.e two nodes in the tree have the same child. Identify the defective node and remove an extra edge to fix the tree.
Example:
Input:
1
/ \
2 3
/ \ /
4 5
Output:
1 1
/ \ / \
2 3 or 2 3
/ \ / /
4 5 4 5
Explanation: We can remove either 3-5 or 2-5.
Solution
public static TreeNode removeEdgeBT(TreeNode root) {
return removeEdgeBT(root, new HashSet<>());
}
private static TreeNode removeEdgeBT(TreeNode node, Set<TreeNode> seen) {
if (node == null || !seen.add(node)) return null;
node.left = removeEdgeBT(node.left, seen);
node.right = removeEdgeBT(node.right, seen);
return node;
}
Follow-up 1:
What if the tree is a BST?
Example:
Input:
3
/ \
2 5
/ \ /
1 4
Output:
3
/ \
2 5
/ /
1 4
Explanation: In this case we can only remove 2-4 because if we remove 5-4 the BST will be invalid.
Hint https://leetcode.com/problems/validate-binary-search-tree
Solution
public static TreeNode removeEdgeBST(TreeNode root) {
return removeEdgeBST(root, null, null);
}
private static TreeNode removeEdgeBST(TreeNode node, Integer min, Integer max) {
if (node == null) return null;
if ((min != null && node.val < min) || (max != null && node.val > max)) return null;
node.left = removeEdgeBST(node.left, min, node.val);
node.right = removeEdgeBST(node.right, node.val, max);
return node;
}
Follow-up 2:
What if the tree is an N-ary tree?