题目

1.same tree

Given two binary trees, write a function to check if they are equal or not.

Two binary trees are considered equal if they are structurally identical and the nodes have the same value.

2.symmetric tree

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

For example, this binary tree is symmetric:

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

But the following is not:

    1
   / \
  2   2
   \   \
   3    3

Note:
Bonus points if you could solve it both recursively and iteratively.

代码

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if(p==null && q==null) return true;
        if(p==null || q==null || q.val!=p.val ) return false;
        if(isSameTree(p.left,q.left)==false || isSameTree(p.right,q.right)==false) return false;
        return true;
    }
}

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isSymmetric(TreeNode root) {
        if (root==null) return true;
        return isEquel(root.left,root.right);
    }
     public boolean isEquel(TreeNode root1,TreeNode root2){
            if(root1==null && root2==null) return true;
            if(root1==null || root2==null) return false;
            if(root1.val!=root2.val) return false;

            return isEquel(root1.left,root2.right) && isEquel(root2.left,root1.right); 

        }
}

代码下载：https://github.com/jimenbian/GarvinLeetCode

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