剑指offer:把二叉树打印成多行

/*
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;
Q.push(pRoot);
Q.push(NULL);

while (!Q.empty()){

if (Q.front() == NULL){
Q.pop();
break;
}

vector<int> level;

while (Q.front()){
TreeNode* front = Q.front();
level.push_back(front->val);
Q.pop();

if (front->left) Q.push(front->left);
if (front->right) Q.push(front->right);
}

res.push_back(level);

Q.pop();
Q.push(NULL);
}

return res;
}

};