题目描述

blablabla

样例

blablabla

算法1(BFS+辅助判断)

/**
 * 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<vector<int>> printFromTopToBottom(TreeNode* root) {
        vector<vector<int> > res;
        if (!root) return res;
        queue<TreeNode*> q;
        q.push(root);
        bool isleft=false;
        while (q.size()) {
            int sz=q.size();
            vector<int> tmp;
            for (int i=0;i<sz;i++) {
                auto cur=q.front();
                q.pop();
                tmp.push_back(cur->val);
                if (cur->left) q.push(cur->left);
                if (cur->right) q.push(cur->right);
            }
            isleft=!isleft;
            if (!isleft) {
                res.push_back(vector<int>(tmp.rbegin(),tmp.rend()));
            }
            else res.push_back(tmp);
        }
        return res;
    }
};