WEI-CHENG CHEN

說明

要做 z 字形便利

解法

就是 BFS，但要設定一格 flag 去判斷是否要顛倒

class Solution {
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
        vector<vector<int>> ans;
        if(!root) return ans;
        queue<TreeNode*> q;
        q.push(root);

        bool flag = true;

        while(!q.empty()){
            int n = q.size();
            vector<int> v;
            for(int i=0;i<n;i++){
                TreeNode* node = q.front();
                q.pop();
                v.push_back(node->val);
                if(node->left)q.push(node->left);
                if(node->right)q.push(node->right);
            }
            if(!flag) reverse(v.begin(), v.end());
            ans.push_back(v);
            flag = !flag;
        }
        return ans;
    }
};