Java BASIC Programming--Tree substructure

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The topic describes the input of two binary trees, a, a, B, to determine whether a sub-structure of a. (PS: We agree that an empty tree is not a sub-structure of any tree) topic code

/*** Enter two binary trees A, B, to determine whether the sub-structure of a. (PS: We agree that the empty tree is not a sub-structure of any tree) * Created by Yukai Fan on 2018/9/3. */ Public classHassubtree { Public Static voidMain (string[] args) {TreeNode a=NewTreeNode (2); A.left=NewTreeNode (4); A.right=NewTreeNode (6); A.left.left=NewTreeNode (7); A.left.right=NewTreeNode (9); A.right.right=NewTreeNode (21); A.right.left=NewTreeNode (14); TreeNode A1=NewTreeNode (2); A1.left=NewTreeNode (4); A1.right=NewTreeNode (6); Booleanb =Hassubtree (A, A1);    System.out.println (b); }     Public Static BooleanHassubtree (TreeNode root1, TreeNode root2) {Booleanresult =false; //Judging premise Two trees are non-empty        if(Root1! =NULL&& Root2! =NULL) {            //if the node that exists ROOT1 is equal to the root node of Root2            if(Root1.val = =root2.val) {//The root node of the Root2 is the starting point to determine whether it contains Root2result =Issubtree (ROOT1, Root2); }            //If you can't find it, go to Root1 's left subtree loop recursion.            if(!result) {Result=Hassubtree (Root1.left, Root2); }            //if Zuozi can not find it, go to Root1 's right subtree loop recursion            if(!result) {Result=Hassubtree (Root1.right, Root2); }        }        returnresult; }     Public Static BooleanIssubtree (TreeNode root1, TreeNode root2) {//returns True if the Root2 has been traversed in root1 .        if(Root2 = =NULL) {            return true; }        //If ROOT1 is finished, and Root2 is not finished, the ROOT1 does not contain Root2 and returns false        if(ROOT1 = =NULL) {            return false; }        //returns False if one of the points does not correspond on        if(Root1.val! =root2.val) {return false; }        //if the root node corresponds, go to the child node and match it separately .        returnIssubtree (Root1.left, Root2.left) &&Issubtree (Root1.right, root2.right); }}

/***/Publicclass  TreeNode    {int  val;    TreeNode left;    TreeNode right;    TreeNode (int  val) {        this. val = val;    }} 

Topic extension

Sub-tree and substructure of binary tree

A subtree means that as long as a node is included, all nodes under that node must be included

The sub-structure means that it contains a node that can take the left subtree or the right subtree, or not take

Simply put, the substructure can be any part of the tree.

Here's a simple example:

such as 1 is 7 nodes, height is 3 of the two fork tree

Figure 1:

　　

The subtree in Figure 1 can be:

The sub-structure of Figure 1 is:

Since the substructure can be any part of the original tree, Figure 4 is a sub-structure.

How to judge the sub-tree of a binary tree

Analysis: Because subtree indicates that if a node is included, all nodes under the node must be included. (so 4, not a tree's subtree.) But sub-structure!!! )

So the code modifies the Code on the Issubtree () based on the above

 Public Static BooleanisSubTree2 (TreeNode root1, TreeNode root2) {/*because subtree indicates that if a node is included, all nodes under the node must be included. So only if Root1 and Root2 both traverse the end are empty, can return true*/        if(ROOT1 = =NULL&& Root2 = =NULL) {            return true; } Else if(Root1! =NULL&& Root2! =NULL) {            if(Root1.val! =root2.val) {return false; }            returnIsSubTree2 (Root1.left,root2.left) &&isSubTree2 (Root1.right, root2.right); } Else {            return false; }    }

Java BASIC Programming--Tree substructure