leetcode:Binary Tree Level Order Traversal 二叉树层序遍历

/** *这是典型的宽度优先算法，利用队列来实现 * **/#include <iostream>#include <vector>#include <queue>using namespace std;struct TreeNode {    int val;    TreeNode *left;    TreeNode *right;    TreeNode(int x) : val(x), left(NULL), right(NULL) {}};//Iterativeclass Solution{public:    vector<vector<int>> levelOrder(TreeNode* root){        vector<vector<int>> res;        if(root==NULL)             return res;        queue<TreeNode*> q;        q.push(root);        while(!q.empty()){            vector<int> oneLevel;            int size=q.size();            for(int i=0;i<size;++i){                TreeNode* node=q.front();                q.pop();                oneLevel.push_back(node->val);                if(node->left) q.push(node->left);                if(node->right) q.push(node->right);            }            res.push_back(oneLevel);        }        return res;    }};int main(){    TreeNode root(3);    TreeNode node1(9);    TreeNode node2(20);    TreeNode node3(15);    TreeNode node4(7);    root.left = &node1;    root.right = &node2;    node2.left = &node3;    node2.right = &node4;    Solution s;    for (const auto &v : s.levelOrder(&root))   //c++11    {        for (auto i : v)            cout << i << " ";        cout << endl;    }    return 0;}