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:
    /**
     * 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* pRoot) {
        // write code here
        vector<vector<int>>res;
        if (!pRoot) {
            return res;//如果pRoot为空，直接返回res
        }
        queue<TreeNode*>q;
        TreeNode* cur;
        q.push(pRoot);//将头指针装入队列
        bool flag=true;//定义一个bool值
        while (!q.empty()) {
            vector<int>v;
            int n = q.size();//定义q的大小
            flag=!flag;//奇数行不反转
            for (int j = 0; j < n; j++) {
                cur = q.front();
                q.pop();
                v.push_back(cur->val);
                if (cur->left) {
                    q.push(cur->left);
                }
                if (cur->right) {
                    q.push(cur->right);
                }
            }
            if(flag){
                reverse(v.begin(),v.end());
            }//偶数行反转
            res.push_back(v);//传入vector
        }
        return res;
    }
};