使用队列以及reverse()函数

/*
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>> vec;
        vector<int> v;
        bool flag=true;
        if(pRoot==NULL){
            return vec;
        }
        queue<TreeNode*> q;
        q.push(pRoot);
        while(!q.empty()){
            int len=q.size();
            for(int i=0;i<len;++i){
                TreeNode *t=q.front();
                q.pop();
                if(!t){//考虑出现空节点情况
                    continue;
                }
                q.push(t->left);
                q.push(t->right);
                
                v.push_back(t->val);
                
            }
            if(flag){
                flag=false;
            }
            else{
                reverse(v.begin(),v.end());
                flag=true;
            }
            if(v.size()){
                vec.push_back(v);
            }
            v.clear();
            
        }
        return vec;
    }
    
};