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。

AC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> > res;
            if (pRoot == NULL) {
                return res;
            }
            queue<TreeNode*> q;
            int len = 0;
            q.push(pRoot);
            TreeNode* node = NULL;
            while (!q.empty()) {
                vector<int> vec;
                len = q.size();
                for (int i = 0;i < len; ++i) {
                    node = q.front();
                    vec.push_back(node->val);
                    if (node->left) {
                        q.push(node->left);
                    }
                    if (node->right) {
                        q.push(node->right);
                    }
                    q.pop();
                }
                res.push_back(vec);
            }
            return res;
        }
};

思路

关键点是找一个变量记录当前层数的结点数量.不能直接使用queue.size(),因为size会变动