二叉树【Java】

二叉树遍历

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前序遍历中序遍历后续遍历

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代码前中后序遍历

package Trww;public class TreeTraversal {/*12   34   5 6*/public static void main(String[] args) {TreeNode tree = new TreeNode(new TreeNode(new TreeNode(4),2,null),1,new TreeNode(new TreeNode(5),3,new TreeNode(6)));preOrder(tree);System.out.println();inorder(tree);System.out.println();postOrder(tree);}
//    前序遍历static void preOrder(TreeNode node){if (node==null){return;}System.out.print(node.val+"\t");//值preOrder(node.left);preOrder(node.right);}
//    中序遍历static void inorder(TreeNode node){if (node==null){return;}inorder(node.left);System.out.print(node.val+"\t");//值inorder(node.right);}
//    后续遍历static void postOrder(TreeNode node){if (node==null){return;}postOrder(node.left);postOrder(node.right);System.out.print(node.val+"\t");//值}
}

对称二叉树

https://leetcode.cn/problems/symmetric-tree/description/

package Trww;public class E04Leetcode101 {public boolean isSymmetric(TreeNode root) {return check(root.left,root.right);}private boolean check(TreeNode left,TreeNode right){if (left==null && right==null){return true;}//判断左右是否为空有一个为空就不对if (right==null||left==null){return false;}//判断里面值if (left.val!=right.val){return false;}//左孩子的左边左孩子和右边的右孩子return check(left.left,right.right) &&check(left.right,right.left);}}

二叉树的最大深度

package Trww;public class E04Leecode104 {static int left=0;static int right=0;public static void main(String[] args) {TreeNode treeNode2 = new TreeNode(3);TreeNode treeNode = new TreeNode(9,treeNode2,treeNode2);System.out.println(maxDepth(treeNode));}static int maxDepth(TreeNode root) {if (root==null){return 0;}int d1 =maxDepth(root.left);int d2 =maxDepth(root.right);return Integer.max(d1,d2)+1;}
}