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SymmetricalBinaryTree.java

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package _28;

import structure.TreeNode;

// 对称的二叉树

// 请实现一个函数，用来判断一棵二叉树是不是对称的。

public class SymmetricalBinaryTree {

public static boolean isSymmetrical(TreeNode root) {

if (root == null) {

return true;

}

return isSymmetrical(root.left, root.right);

}

public static boolean isSymmetrical(TreeNode r1, TreeNode r2) {

if (r1 == null && r2 == null) {

return true;

}

if (r1 == null || r2 == null) {

return false;

}

if (r1.val != r2.val) {

return false;

}

return isSymmetrical(r1.left, r2.right) && isSymmetrical(r1.right, r2.left);

}

public static void main(String[] args) {

// 8

// 6 6

// 5 7 7 5

TreeNode root = new TreeNode(8);

root.left = new TreeNode(6);

root.right = new TreeNode(6);

root.left.left = new TreeNode(5);

root.left.right = new TreeNode(7);

root.right.left = new TreeNode(7);

root.right.right = new TreeNode(5);

System.out.println(isSymmetrical(root));

System.out.println(isSymmetrical(root.left));

}

}