Leetcode226(翻转二叉树)

package tree;import java.util.Deque;
import java.util.LinkedList;public class LeetCode226 {public static void main(String[] args) {System.out.print("待定");}//递归public static void invertTree(TreeNode root) {if(root==null) {return;}swap(root);invertTree(root.left);invertTree(root.right);}public static void swap(TreeNode root) {TreeNode temp = root.right;root.right = root.left;root.left = temp;}//迭代public static void invertTree02(TreeNode root) {Deque<TreeNode> de = new LinkedList<>();if(root ==null) {return;}de.addFirst(root);while(!de.isEmpty()) {TreeNode temp = de.peekFirst();swap(temp);de.pollFirst();de.addFirst(temp.right);de.addFirst(temp.left);}}
}

Leetcode101(对称二叉树)

class Solution {public boolean isSymmetric(TreeNode root) {return compare(root.left,root.right);}public static boolean compare(TreeNode left,TreeNode right) {if(left==null&&right!=null)return false;else if(right==null&&left!=null)return false;else if(right==null&&left==null)return true;else if(left.val!=right.val)return false;boolean outsize = compare(left.left,right.right);boolean insize = compare(left.right,right.left);return outsize&&insize;}//迭代法public boolean isSymmetric(TreeNode root) {if(root==null) {return true;}Deque<TreeNode> de = new LinkedList<>();de.addLast(root.left);de.addLast(root.right);while(!de.isEmpty()) {TreeNode left = de.peekFirst();de.pollFirst();TreeNode right = de.peekFirst();de.pollFirst();if(left==null&&right==null) {continue;}if(left==null||right==null||(left.val!=right.val)) {return false;}de.addLast(left.left);de.addLast(right.right);de.addLast(left.right);de.addLast(right.left);}return true;}}