【LeetCode】 101. Symmetric Tree (Easy) (JAVA)

【LeetCode】 101. Symmetric Tree (Easy) (JAVA)

Title address: https://leetcode.com/problems/symmetric-tree/

Title description:

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

    1
   / \
  2   2
 / \ / \
3  4 4  3

But the following [1,2,2,null,3,null,3] is not:

    1
   / \
  2   2
   \   \
   3    3

Follow up: Solve it both recursively and iteratively.

Topic

Given a binary tree, check whether it is mirror-symmetrical.

Problem solving method

1. Use the recursive method
2. Find the recursive conditions, left.left == right.right, left.right == right.left

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isSymmetric(TreeNode root) {
        if (root == null) return true;
        return iH(root.left, root.right);
    }

    public boolean iH(TreeNode left, TreeNode right) {
        if (left == null || right == null) return left == right;
        return left.val == right.val && iH(left.left, right.right) && iH(left.right, right.left);
    }
}

Execution time: 0 ms, defeated 100.00% of users
in all Java submissions Memory consumption: 37.8 MB, defeated 36.25% of users in all Java submissions

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Origin blog.csdn.net/qq_16927853/article/details/105731271