Create tree from Inorder and Preorder

Author: akashmodak97

Hacker Blocks/Create tree from Inorder and Preorder.cpp

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+/* Hacker Blocks */
+/* Title - Level Order (ZigZag) */
+/* Created By - Akash Modak */
+/* Date - 19/09/2020 */
+
+// Given preorder and inorder create the tree
+
+// Input Format
+// Enter the size of the preorder array N then add N more elements and store in the array denoting the preorder traversal of the tree. Then enter the size of the inorder array M and add M more elements and store the inorder traversal of the array.
+
+// Constraints
+// 1 <= N, M <= 10^4
+
+// Output Format
+// Display the tree using a modified preorder function. For each node , first print its left child's data , then the data of the root itself , then the data of its right child. Do this for each node in a new line in preorder manner. If one of the children does not exist print END in its place. Refer to the sample testcase.
+
+// Sample Input
+// 3
+// 1 2 3
+// 3
+// 3 2 1
+// Sample Output
+// 2 => 1 <= END
+// 3 => 2 <= END
+// END => 3 <= END
+// Explanation
+// The above tree looks like
+
+//          1
+//        /
+//      2
+//    /
+//  3
+
+#include<bits/stdc++.h>
+using namespace std;
+class node{
+	public:
+	int data;
+	node *left,*right;
+	node(int d){
+		data = d;
+		left=right=NULL;
+	}
+};
+
+node* build(int pre[],int in[],int start,int end,int &preIndex){
+	if(start>end){
+		return NULL;
+	}
+
+	node* root = new node(pre[preIndex]);
+	
+	int i;
+	for(i=start;i<=end;i++)
+	if(pre[preIndex]==in[i])
+	break;
+	preIndex++;
+	root->left = build(pre,in,start,i-1,preIndex);
+	root->right = build(pre,in,i+1,end,preIndex);
+	return root;
+}
+void modifiedPreorder(node* root){
+	if(root==NULL)
+	return;
+	if(root->left)
+	cout<<root->left->data<<" => ";
+	else
+	cout<<"END => ";
+	cout<<root->data;
+	if(root->right)
+	cout<<" <= "<<root->right->data<<endl;
+	else
+	cout<<" <= END "<<endl;
+	
+	modifiedPreorder(root->left);
+	modifiedPreorder(root->right);
+	return;
+}
+int main() {
+	int n;
+	cin>>n;
+	int pre[n],in[n];
+	for(int i=0;i<n;i++)
+	cin>>pre[i];
+
+	cin>>n;
+	for(int i=0;i<n;i++)
+	cin>>in[i];
+	// 	for(int i=0;i<n;i++)
+	// cout<<in[i]<<" ";
+	// cout<<endl;
+	int m=0;
+	node* root=build(pre,in,0,n-1,m);
+	// cout<<root->data;
+	modifiedPreorder(root);
+	return 0;
+}