把二叉树打印成多行

题目描述

从上到下按层打印二叉树，同一层结点从左至右输出。每一层输出一行。

代码

/*
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) {
		vector<vector<int> > ans;
        if (pRoot != NULL) {
            vector<int> vet;
            queue<TreeNode*> que;
            
            que.push(pRoot);
            que.push(NULL);
            
            TreeNode* cur;
            while (!que.empty()) {
                cur = que.front();
                que.pop();
                if (cur == NULL) {
                    ans.push_back(vet);
                    vet.clear();
                    if (!que.empty()) {
                        que.push(NULL);
                    }
                } else {
                    vet.push_back(cur->val);
                    if (cur->left != NULL) {
                        que.push(cur->left);
                    }
                    if (cur->right != NULL) {
                        que.push(cur->right);
                    }
                }
            }
           
        }
        return ans;
    }
    
};