LeetCode：226翻转二叉树

方法一递归法/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val val; * this.left left; * this.right right; * } * } */ class Solution { public TreeNode invertTree(TreeNode root) { if(root null){ return null; } //左右节点交换 TreeNode temp root.right; root.right root.left; root.left temp; //递归左右节点 invertTree(root.left); invertTree(root.right); return root; } }方法二/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val val; * this.left left; * this.right right; * } * } */ class Solution{ public TreeNode invertTree(TreeNode root){ if(root null){ return null; } QueueTreeNode queue new LinkedList(); queue.offer(root); while(!queue.isEmpty()){ TreeNode current queue.poll(); //交换左右节点 TreeNode temp current.left; current.left current.right; current.right temp; //左右节点不为空则入队 if(current.left ! null){ queue.offer(current.left); } if(current.right ! null){ queue.offer(current.right); } } return root; } }迭代法思路先将根节点入队while循环只要队列不为空就交换当前要出队节点的左右节点然后判断当前出队节点的下面是否还有左右节点如果有就继续入队循环。爆栈层序遍历逐层打印。寻找最短路径使用队列核心new Queue - offer(root) - while(!isEmpty) - poll() - 处理逻辑 - offer(children)