Invert a binary tree.
4 / \ 2 7 / \ / \1 3 6 9
to4 / \ 7 2 / \ / \9 6 3 1
Trivia:This problem was inspired by this original tweet by Max Howell:Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so fuck off.
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题目
翻转一棵二叉树
分析
Approach #1 (Recursive) [Accepted]
递归交换左右子树即可
public TreeNode invertTree(TreeNode root) {
if (root == null) {
return null;
}
TreeNode right = invertTree(root.right);
TreeNode left = invertTree(root.left);
root.left = right;
root.right = left;
return root;
}
Approach #2 (Iterative) [Accepted]
利用一个队列即可，就像是层次遍历，不过在里面多加入一个交换的操作
public TreeNode invertTree(TreeNode root) {
if (root == null) return null;
Queue<TreeNode> queue = new LinkedList<TreeNode>();
queue.add(root);
while (!queue.isEmpty()) {
TreeNode current = queue.poll();
TreeNode temp = current.left;
current.left = current.right;
current.right = temp;
if (current.left != null) queue.add(current.left);
if (current.right != null) queue.add(current.right);
}
return root;
}
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