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(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    vector<vector<int> > Print(TreeNode* pRoot) {
        if (pRoot == nullptr) return {};
        bool flag = false;
        vector<vector<int>> res;
        deque<TreeNode*> de;
        de.push_back(pRoot);
        while (!de.empty()) {
            int size = de.size();
            vector<int> temp;
            if (flag) {
                for (int i=0; i<size; ++i) {
                    TreeNode* node = de.back();
                    de.pop_back();
                    temp.emplace_back(node->val);
                    if (node->right) {
                        de.push_front(node->right);
                    }
                    if (node->left) {
                        de.push_front(node->left);
                    }
                }
                flag = false;                
            } else {
                for (int i=0; i<size; ++i) {
                    TreeNode* node = de.front();
                    de.pop_front();
                    temp.emplace_back(node->val);
                    if (node->left) {
                        de.push_back(node->left);
                    }
                    if (node->right) {
                        de.push_back(node->right);
                    }
                }
                flag = true;
            }
            res.push_back(temp);
        }
            return res;
    }
};