leetcode笔记-层序遍历

/** * 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<int> a;        vector<vector<int>> b;        queue<TreeNode*> s;        s.push(root);        int level=1;        if(root==NULL) return b;        else         {                        while(!s.empty())            {               TreeNode *cur;               queue<TreeNode *> nxtlevel;               while(!s.empty())                {                    TreeNode *cur=s.front();                    s.pop();                    a.push_back(cur->val);                    if(cur->left!=NULL) nxtlevel.push(cur->left);                    if(cur->right!=NULL) nxtlevel.push(cur->right);                                    }                b.push_back(a);                s=nxtlevel;                 a.clear();                             }             return b;                     }             }      };