二叉树的镜像。
226. Invert Binary Tree
Invert a binary tree.
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4
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2 7
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1 3 6 9
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to
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4
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7 2
/ /
9 6 3 1
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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 f*** off.
算法：基于二叉树的层次遍历算法，翻转每个节点的左右子树
算法1迭代算法，Leetcode 1ms：
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public TreeNode (TreeNode root) {
if (root == null) return null;
ArrayDeque<TreeNode> queue = new ArrayDeque<>();
queue.offer(root);
while (!queue.isEmpty()) {
int size = queue.size();
for (int i = 0; i < size; i++) {
TreeNode p = queue.poll();
if (p.left != null) queue.offer(p.left);
if (p.right != null) queue.offer(p.right);
TreeNode tmp = p.left;
p.left = p.right;
p.right = tmp;
}
}
return root;
}
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算法2递归算法，Leetcode 0ms：
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public TreeNode (TreeNode root) {
if(root == null || (root.left == null && root.right == null)) return root;
TreeNode tmp = root.left;
root.left = invertTree(root.right);
root.right = invertTree(tmp);
return root;
}
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