题解 | #按之字形顺序打印二叉树#

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};
*/
class Solution {
  public:
    vector<vector<int> > Print(TreeNode* pRoot) {
        vector<vector<int>> ret;
        if (pRoot == nullptr) {
            return ret;
        }
        deque<TreeNode*> treeDeque;
        treeDeque.push_back(pRoot);
        int direction = 1;
        while (!treeDeque.empty()) 
        {
            int num = treeDeque.size();
            vector<int> lineData;
            for (int i = 0; i < num; ++i) 
            {
                if (direction)
                {
                    TreeNode* temNode = treeDeque.front();
                    treeDeque.pop_front();
                    if(temNode->left)
                    {
                        treeDeque.push_back(temNode->left);
                    }
                    if(temNode->right)
                    {
                        treeDeque.push_back(temNode->right);
                    }
                    lineData.push_back(temNode->val);
                } 
                else 
                {
                    TreeNode* temNode=treeDeque.back();
                    treeDeque.pop_back();
                    if(temNode->right)
                    {
                        treeDeque.push_front(temNode->right);
                    }
                    if(temNode->left)
                    {
                        treeDeque.push_front(temNode->left);
                    }
                    lineData.push_back(temNode->val);
                }
            }
            ret.emplace_back(lineData);
            direction=direction==1?0:1;
        }
        return ret;

    }

};