Leetcode 101. Symmetric Tree

文章作者:Tyan
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1. Description

Symmetric Tree

2. Solution

  • Recursive
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/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
bool isSymmetric(TreeNode* root) {
if(root == NULL) {
return true;
}
return isMirror(root->left, root->right);
}
bool isMirror(TreeNode* left, TreeNode* right) {
if(left == NULL && right == NULL) {
return true;
}
if(left == NULL || right == NULL) {
return false;
}
return left->val == right->val && isMirror(left->left, right->right) && isMirror(left->right, right->left);
}
};
  • Iterative
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    /**
    * Definition for a binary tree node.
    * struct TreeNode {
    * int val;
    * TreeNode *left;
    * TreeNode *right;
    * TreeNode(int x) : val(x), left(NULL), right(NULL) {}
    * };
    */
    class Solution {
    public:
    bool isSymmetric(TreeNode* root) {
    if(root == NULL) {
    return true;
    }
    queue<TreeNode*> nodes;
    nodes.push(root);
    nodes.push(root);
    while(!nodes.empty()) {
    TreeNode* left = nodes.front();
    nodes.pop();
    TreeNode* right = nodes.front();
    nodes.pop();
    if(left == NULL && right == NULL) {
    continue;
    }
    if(left == NULL || right == NULL) {
    return false;
    }
    if(left->val == right->val) {
    nodes.push(left->left);
    nodes.push(right->right);
    nodes.push(left->right);
    nodes.push(right->left);
    }
    else {
    return false;
    }
    }
    return true;
    }
    };

Reference

  1. https://leetcode.com/problems/symmetric-tree/description/
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