题目传送门

题解

• 和JZ60.把二叉树打印成多行是一样的，只不过偶数行逆序。
• 偶数行的时候多个反转步骤即可

AC-Code

/*
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) {
        queue<TreeNode*> que;
        vector<vector<int> > ans;
        if(pRoot)    que.push(pRoot);
        bool flag = false; // true:偶数行，false:奇数行
        while(!que.empty()) {
            int sz = que.size();
            vector<int> res;
            while(sz--) {
                TreeNode *pnode = que.front();
                que.pop();
                res.push_back(pnode->val);
                if(pnode->left)    que.push(pnode->left);
                if(pnode->right)    que.push(pnode->right);
            }
            if(flag ) 
                reverse(res.begin(), res.end());
            ans.push_back(res);
            flag = !flag;
        }
        return ans;
    }
};