剑指offer 23：从上往下打印二叉树

/*
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> result;
        //申请一个队列专门放横排的数据
        if (root==NULL){
            return result;
        }
        queue<TreeNode*> que;
        
        que.push(root); 
        while(!que.empty()){
            if(root->left!=NULL){
                que.push(root->left);
            }
            if(root->right!=NULL){
                que.push(root->right); 
            }
            int val=root->val;
            result.push_back(val);
            que.pop();
            root=que.front();
        }
          return result;
    }
  
};