# Make a Binary Tree from Given Inorder and Preorder Traveral.

Objective: Given a inorder and preorder traversal, construct a binary tree from that.

Input: Inorder and preorder traversals

Similar Problem: Construct a binary tree from given Inorder and Postorder Traversal

Approach:

int [] inOrder = {2,5,6,10,12,14,15};

int [] preOrder = {10,5,2,6,14,12,15};

• First element in preorder[] will be the root of the tree, here its 10.
• Now the search element 10 in inorder[], say you find it at position i, once you find it, make note of elements which are left to i (this will construct the leftsubtree) and elements which are right to i ( this will construct the rightSubtree).
• See this step above and recursively construct left subtree and link it root.left and recursively construct right subtree and link it root.right.

• See the picture and code.

Complete Code:

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 public class MakeTreefromInorderAndPreorder { public static int pIndex=0; public Node makeBTree(int [] inOrder, int [] preOrder, int iStart, int iEnd ){ if(iStart>iEnd){ return null; } Node root = new Node(preOrder[pIndex]);pIndex++; if(iStart==iEnd){ return root; } int index = getInorderIndex(inOrder, iStart, iEnd, root.data); root.left = makeBTree(inOrder,preOrder,iStart, index–1); root.right = makeBTree(inOrder,preOrder,index+1, iEnd); //} return root; } public int getInorderIndex(int [] inOrder, int start, int end, int data){ for(int i=start;i<=end;i++){ if(inOrder[i]==data){ return i; } } return –1; } public void printINORDER(Node root){ if(root!=null){ printINORDER(root.left); System.out.print(" " + root.data); printINORDER(root.right); } } public static void main (String[] args) throws java.lang.Exception { int [] inOrder = {2,5,6,10,12,14,15}; int [] preOrder = {10,5,2,6,14,12,15}; MakeTreefromInorderAndPreorder i = new MakeTreefromInorderAndPreorder(); Node x = i.makeBTree(inOrder, preOrder, 0, inOrder.length–1); System.out.println("Constructed Tree : "); i.printINORDER(x); } } class Node{ int data; Node left; Node right; public Node (int data){ this.data = data; left = null; right = null; } }

Output:

```Constructed Tree :
2  5  6  10  12  14  15```

### 2 thoughts on “Make a Binary Tree from Given Inorder and Preorder Traveral.”

1. Broken method.

No solution for —

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