题解 | #判断二叉树是否对称#

递归

class Solution {
public:
    //递归
    bool isSymmetric(TreeNode* root) {
        // write code here
        if(!root) return true;
        return isSymmetric_(root->left, root->right);
    }
    bool isSymmetric_(TreeNode* l, TreeNode* r){
        if(!l && !r) return true;
        if(!l || !r) return false;
        if(l->val != r->val)
            return false;
        return isSymmetric_(l->left, r->right) &&
            isSymmetric_(l->right, r->left);
    }
};

非递归

class Solution {
public:
    //非递归
    bool isSymmetric(TreeNode* root) {
        // write code here
        if (!root || !root->left && !root->right)
            return true;
        queue<TreeNode*> q;
        q.push(root->left);
        q.push(root->right);
        while (!q.empty()) {
            int sz = q.size();
            for (int i = 0; i < sz; i += 2) {
                TreeNode* L = q.front();
                q.pop();
                TreeNode* R = q.front();
                q.pop();
                if (!L && !R) continue;
                else if (!L || !R) return false;
                else if (L->val != R->val) return false;
                q.push(L->left);
                q.push(R->right);
                q.push(L->right);
                q.push(R->left);
            }
        }
        return true;
    }
};