【LeetCode】Symmetric Tree

101. Symmetric Tree

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

 

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

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
//比较对称节点值是否相同
bool isSameCompare(struct TreeNode* root, int value)
{
    if(root->val == value)
    {
        return true;
    }
    else
    {
        return false;
    }
}
//比较结构是否对称
bool isSameLeft(struct TreeNode* rootLeft, struct TreeNode* rootRight)
{
    //结构不同返回false
    if((!rootLeft && rootRight) || (rootLeft && !rootRight))
    {
        return false;
    }
    //叶子节点结束证明已比较的是对称的
    if(!rootLeft && !rootRight)
    {
        return true;
    }
    if( !isSameCompare(rootRight, rootLeft->val) )
    {
        return false;
    }
    //递归求根节点下的左子树和右子树是否对称
    return (isSameLeft(rootLeft->left, rootRight->right) && isSameLeft(rootLeft->right, rootRight->left));
}
bool isSymmetric(struct TreeNode* root) 
{
    if(!root)
    {
        return true;
    }
    return isSameLeft(root->left, root->right);
}

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