Leetcode 94. Binary Tree inorder traversal (middle sequence traversal binary trees)

Given a binary tree, return the inorder traversal of its nodes ' values.

For Example:given binary Tree [1,null,2,3] ,

   1         2    /   3

Return [1,3,2] .

Note: Recursive (Recursive) solution is trivial, could do it iteratively (iteration)?

Ideas:

Solution One: The recursive method is very simple,

(1) If root is empty, NULL is returned;

(2) If Root->left = NULL, returns the middle-order traversal element of the left subtree;

(3) If root->right = NULL, returns the middle-order traversal element of the right subtree;

(4) Finally, the left sub-tree in the middle sequence traversal elements into the container, root->val into the container, and then the right subtree of the middle sequence traversal elements into the container;

(5) Return to the container;

1 /**2 * Definition for a binary tree node.3 * struct TreeNode {4 * int val;5 * TreeNode *left;6 * TreeNode *right;7 * TreeNode (int x): Val (x), left (null), right (null) {}8  * };9  */Ten classSolution { One  Public: Avector<int> Inordertraversal (treenode*root) { -vector<int>V, v1, v2; -         inti; the         if(Root = =NULL) -            returnv; -         if(Root->left! =NULL) -V1 = inordertraversal (root->Left ); +         if(Root->right! =NULL) -V2 = Inordertraversal (root->Right ); +          for(i =0; I < v1.size (); i++) A V.push_back (V1[i]); atV.push_back (root->val); -          for(i =0; I < v2.size (); i++) - V.push_back (V2[i]); -         returnv; -}

Solution Two: Non-recursive middle sequence traversal binary tree, to define a stack (stack)

1 classSolution {2  Public:3vector<int> Inordertraversal (treenode*root) {4vector<int>v;5Stack<treenode*>Node_stack;6treenode* Pnode =Root;7          while((Pnode! = NULL) | |!Node_stack.empty ()) {8             //node is not empty, joins the stack, and accesses the left subtree of the node9             if(Pnode! =NULL) {Ten Node_stack.push (pnode); OnePnode = pnode->Left ; A             } -             Else{ -                 //The node is empty, pops a node from the stack, accesses the node, thePnode =node_stack.top (); - Node_stack.pop (); -V.push_back (pnode->val); -                 //Access node right subtree +Pnode = pnode->Right ; -             } +         } A         returnv; at     } -};

Leetcode 94. Binary Tree inorder traversal (middle sequence traversal binary trees)