LeetCode系列101—对称二叉树

题意

101. 对称二叉树

题解

方法一：递归

class Solution {
    
    
public:
    bool check(TreeNode *p, TreeNode *q) {
    
    
        if (!p && !q) return true;
        if (!p || !q) return false;
        return p->val == q->val && check(p->left, q->right) && check(p->right, q->left);
    }

    bool isSymmetric(TreeNode* root) {
    
    
        return check(root, root);
    }
};

方法二：迭代

class Solution {
    
    
public:
    bool check(TreeNode *u, TreeNode *v) {
    
    
        queue <TreeNode*> q;
        q.push(u); q.push(v);
        while (!q.empty()) {
    
    
            u = q.front(); q.pop();
            v = q.front(); q.pop();
            if (!u && !v) continue;
            if ((!u || !v) || (u->val != v->val)) return false;

            q.push(u->left); 
            q.push(v->right);

            q.push(u->right); 
            q.push(v->left);
        }
        return true;
    }

    bool isSymmetric(TreeNode* root) {
    
    
        return check(root, root);
    }
};

参考

对称二叉树