Cinte's Leetcode Record
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103. Binary Tree Zigzag Level Order Traversal

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Symbols count in article: 2.6k Reading time ≈ 2 mins.

103. Binary Tree Zigzag Level Order Traversal

使用双向队列，每次都变向
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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
        if(!root)
            return {};
        vector<vector<int>> ret;
        deque<TreeNode*> s;
        s.push_back(root);
        bool left = false;
        int l = 1;
        while(!s.empty())
        {
            int t = s.size();
            vector<int> tmp;
            while(t-- > 0)
            {
                TreeNode* p;
                if(left)
                {
                    p = s.front();
                    s.pop_front();
                    if(p->right)
                        s.push_back(p->right);
                    if(p->left)
                       s.push_back(p->left);
                }else
                {
                    p = s.back();
                    s.pop_back();
                    if(p->left)
                        s.push_front(p->left);
                    if(p->right)
                       s.push_front(p->right);
                }
                tmp.push_back(p->val);
            }
            ret.push_back(tmp);
            left = !left;
        }
        return ret;
    }
};

review

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
        if(!root)
            return {};
        deque<TreeNode*> dq;
        dq.push_back(root);
        vector<vector<int>> ret;
        while(!dq.empty())
        {
            ret.emplace_back();
            for(int i = 0, sz = dq.size(); i < sz; ++i)
            {
                auto node = dq.front();
                dq.pop_front();
                if(node->left)
                    dq.push_back(node->left);
                if(node->right)
                    dq.push_back(node->right);
                ret.back().push_back(node->val);
            }
            if(dq.empty())
                break;
            ret.emplace_back();
            for(int i = 0, sz = dq.size(); i < sz; ++i)
            {
                auto node = dq.back();
                dq.pop_back();
                if(node->right)
                    dq.push_front(node->right);
                if(node->left)
                    dq.push_front(node->left);
                ret.back().push_back(node->val);
            }
        }
        return ret;
    }
};