(C++实现)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> a;
    queue<TreeNode *> tree;
    if(root==NULL)return a;
    TreeNode* r;
    tree.push(root);
    while(tree.size()){
        r=tree.front();
        a.push_back(r->val);
        if(r->left!=NULL){
            tree.push(r->left);
        }
        if(r->right!=NULL){
            tree.push(r->right);
        }
        tree.pop();
    }
     return a;
    }
};