二叉树的多种 顺序遍历

//中序

class Solution {    /**     * @param root: The root of binary tree.     * @return: Inorder in vector which contains node values.     */public:    vector<int> a;    void look(TreeNode *root)    {         if(root==NULL)        return;        look(root->left);        a.push_back(root->val);        look(root->right);    }    vector<int> inorderTraversal(TreeNode *root)     {            look(root);        return a;        // write your code here    }};

//层次遍历

 #include<queue>class Solution {    /**     * @param root: The root of binary tree.     * @return: Level order a list of lists of integer     */public:   vector<vector<int>> a;    vector<vector<int>> levelOrder(TreeNode *root)     {     queue<TreeNode *> q;     if(root==NULL)     return a;     q.push(root);     TreeNode *a1;    a1=new TreeNode;          vector<int> xx;     while(!q.empty())     {          xx.clear();         int x=q.size();          for(int j=0;j<x;j++)         {             a1=q.front();             q.pop();             int t=a1->val;             xx.push_back(t);             if(a1->left!=NULL)                 q.push(a1->left);             if(a1->right!=NULL)                 q.push(a1->right);         }         a.push_back(xx);     }     return a;        // write your code here    }};

后续遍历

class Solution {    /**     * @param root: The root of binary tree.     * @return: Postorder in vector which contains node values.     */public:     vector<int> a;     void look(TreeNode *root)     {         if(root==NULL)         return ;         look(root->left);         look(root->right);         a.push_back(root->val);     }    vector<int> postorderTraversal(TreeNode *root) {        look(root);        return a;        // write your code here    }};