面试题23 从上往下打印二叉树

题目描述

从上往下打印出二叉树的每个节点，同层节点从左至右打印。

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
class Solution {
public:
    vector<int> PrintFromTopToBottom(TreeNode *root) {
        vector<int> v;
        queue<TreeNode *> q;
        TreeNode *p = root;
        while (p || !q.empty()){
            v.push_back(p->val);
            if (p->left)
                q.push(p->left);
            if (p->right)
                q.push(p->right);
            if (q.empty())
                break;
            p = q.front();
            q.pop();
        }
        return v;
    }
};