二叉树的层序遍历（非递归）

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<vector<int>> levelOrder(TreeNode* root) {
vector<vector<int>> result;
if(root==NULL)
return result;

vector<int> level;
queue<const TreeNode*> cur,next;
const TreeNode *node=root;
cur.push(node);

while(!cur.empty())
{
while(!cur.empty())
{
node=cur.front();
cur.pop();
level.push_back(node->val);
if(node->left)
next.push(node->left);
if(node->right)
next.push(node->right);
}
result.push_back(level);
level.clear();
swap(cur,next);
}
//reverse(result.begin(),result.end());

return result;
}
};