LetCode 103. 二叉树的锯齿形层次遍历

/**
 * 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:
    vector> zigzagLevelOrder(TreeNode* root) {
        vector> res;
        if (root == NULL)
            return res;
        // 这里换成双向队列，方便对头或尾进行操作
        deque dq;
        dq.push_back(root);
        bool direction = true;
        while(!dq.empty()){
            // 这层树的节点个数
            int nums = dq.size();
            vector v;
            for (int i = 0; i < nums; i++){
                // 设置了一个变量来控制从左向右还是从右向左
                if (direction){
                    TreeNode* tmp = dq.front();
                    dq.pop_front();
                    if (tmp->left != NULL)
                        dq.push_back(tmp->left);
                    if (tmp->right != NULL)
                        dq.push_back(tmp->right);
                    v.push_back(tmp->val);
                }else{  
                    TreeNode* tmp = dq.back();
                    dq.pop_back();
                    if (tmp->right != NULL)
                        dq.push_front(tmp->right);
                    if (tmp->left != NULL)
                        dq.push_front(tmp->left);
                    v.push_back(tmp->val);
                }
            }
            res.push_back(v);
            direction = !direction;
        }
        return res;
    }
};

static int x=[](){
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();