把二叉树打印成多行

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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。

解题思路

这是二叉树的层序遍历，直接使用构造队列(queue)，来实现每层打印。

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> > result;
        if (pRoot == NULL)
            return result;
        
        queue<TreeNode*> Q;
        Q.push(pRoot);
        while (!Q.empty())
        {
            vector<int> temp;
            int num = Q.size();
            for (int i = 0; i < num; i++)
            {
                TreeNode* front = Q.front();
                if (front->left != NULL)
                    Q.push(front->left);
                if (front->right != NULL)
                    Q.push(front->right);
                temp.push_back(front->val);
                Q.pop();
            }
            if (!temp.empty())
                result.push_back(temp);
        }
        return result;
    }
};