题解 | #按之字形顺序打印二叉树(队列)#

/**
 * struct TreeNode {
 *  int val;
 *  struct TreeNode *left;
 *  struct TreeNode *right;
 *  TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param pRoot TreeNode类
     * @return int整型vector<vector<>>
     */
    vector<vector<int> > Print(TreeNode* root) {
        vector<vector<int>> res;
        bool evenflag = true; //偶层数标志
        queue<TreeNode*> q;
        q.push(root);

        if(root == nullptr) return res;

        while (!q.empty()) {
            int number = q.size(); //每层结点个数
            vector<int> cur;

            for (int i = 0; i < number; i++) {
                TreeNode* node = q.front();
                int value = node->val;
                cur.push_back(value);
                q.pop();
                if (node->left != nullptr) q.push(node->left);
                if (node->right != nullptr) q.push(node->right);
            }
            if (!evenflag) {
                reverse(cur.begin(), cur.end());
            }
            evenflag = !evenflag;
            res.push_back(cur);
        }
        return res;
    }
};

层序遍历的过程中加上一个偶层数的标志