Binary tree generation of two-fork tree based on the first ordinal group of binary tree and the sequence traversal array

Title: The pre-sequence traversal and the middle sequence traversal of a given binary tree, generating a two-fork tree.

Example:

Pre-sequence traversal array: prearr[]:{1,2,4,5,3,6,7}

Middle Sequence Traversal array: inarr[]:{4,2,5,1,6,3,7}

The resulting two fork tree is as follows:

Problem Solving Ideas:

By the nature of the pre-order variables of the two-fork tree: Prearr[0] is the root of the array, there is a binary tree according to the nature of the sequence traversal, {4,2,5} is a two-tree left subtree, {6,3,7} on the right subtree, repeat the operation of the two-tree

 Public classSolution { PublicTreeNode Reconstructbinarytree (int[] Pre,int[] in) {TreeNode root=NewTreeNode (Pre[0]);//the first number of the preamble is determined to be the root        intLen =pre.length; //when there's only one number        if(len = = 1) {Root.left=NULL; Root.right=NULL; returnRoot; }        //find the root position in the middle order        intRootval =Root.val; inti;  for(i = 0; i < Len; i++) {            if(Rootval = =In[i]) Break; }        //Create a left sub-tree        if(I > 0) {            int[] PR =New int[i]; int[] ino =New int[i];  for(intj = 0; J < I; J + +) {Pr[j]= Pre[j + 1]; }             for(intj = 0; J < I; J + +) {Ino[j]=In[j]; } root.left=reconstructbinarytree (PR, INO); } Else{root.left=NULL; }        //Create right subtree        if(Len-i-1 > 0) {            int[] PR =New int[Len-i-1]; int[] ino =New int[Len-i-1];  for(intj = i + 1; J < Len; J + +) {ino[j-I-1] =In[j]; Pr[j-I-1] =Pre[j]; } root.right=reconstructbinarytree (PR, INO); } Else{root.right=NULL; }        returnRoot; }     Public Static voidMain (string[] args) {int[] Prearr = {1, 2, 4, 5, 3, 6, 7}; int[] Inarr = {4, 2, 5, 1, 6, 3, 7}; Solution S=Newsolution (); TreeNode Root=S.reconstructbinarytree (Prearr, Inarr);    S.postorder (root); }

Binary tree generation of two-fork tree based on the first ordinal group of binary tree and the sequence traversal array