From 7afe26d5055741ff04d81ac901b721f15ee600bf Mon Sep 17 00:00:00 2001
From: Ritish Sehgal <59483233+apex-blaze@users.noreply.github.com>
Date: Tue, 13 Apr 2021 20:30:41 +0530
Subject: [PATCH] Added build Binary Tree function in Cpp (#160)

* added max subarray sum

* added pre,in,post traversals

* Update pre-in-post-traversal.cpp

formatted the output

* Update pre-in-post-traversal.cpp

formatted output

* added build binary tree function

Co-authored-by: Arsenic <54987647+Arsenic-ATG@users.noreply.github.com>
---
 trees/README.md                      |  1 +
 trees/c-or-cpp/build-binary-tree.cpp | 99 ++++++++++++++++++++++++++++
 2 files changed, 100 insertions(+)
 create mode 100644 trees/c-or-cpp/build-binary-tree.cpp

diff --git a/trees/README.md b/trees/README.md
index 88fa780e..69807e1d 100644
--- a/trees/README.md
+++ b/trees/README.md
@@ -4,3 +4,4 @@
 
 1. [Pre, In & Post Order Traversals](c-or-cpp/pre-in-post-traversal.cpp)
 2. [Level Order Traversal](c-or-cpp/level-order-traversal.cpp)
+3. [Build Binary Tree using Pre,In & Post Order](c-or-cpp/build-binary-tree.cpp)
diff --git a/trees/c-or-cpp/build-binary-tree.cpp b/trees/c-or-cpp/build-binary-tree.cpp
new file mode 100644
index 00000000..ba524c95
--- /dev/null
+++ b/trees/c-or-cpp/build-binary-tree.cpp
@@ -0,0 +1,99 @@
+#include<iostream>
+#define endl "\n"
+using namespace std;
+
+
+// Basic Structure of a Tree
+struct Node{
+    int data;
+    struct Node *left;
+    struct Node *right;
+
+    Node(int val){
+        data = val;
+        left = NULL;
+        right = NULL;
+    }
+};
+
+/* Construct a binary tree using Pre, In and Post order traversals */
+/* Complexity in Both cases : O(n^2) */
+
+// Utility function to search the element in Inorder
+int search (int in[],int start ,int end,int curr){
+    for(int i=start;i<=end;++i){
+        if(in[i] == curr) 
+         return i;
+    }
+    return -1; 
+}
+
+// Build a binary Tree using Pre & In order (using Recursion)
+Node* buildTreePreIn(int pre[],int in[],int start, int end){
+    static int idx = 0;
+    if(start > end)
+     return NULL;
+
+    int curr = pre[idx]; 
+    idx++;
+    Node* node = new Node(curr);
+
+    if(start == end)
+     return node;
+
+    int pos = search(in,start,end,curr);
+    node->left = buildTreePreIn(pre,in,start,pos-1);
+    node->right = buildTreePreIn(pre,in,pos+1,end);
+
+    return node;
+}
+
+// Build a binary Tree using Post & In order (using Recursion)
+Node* buildTreePostIn(int post[],int in[],int start,int end){
+    static int idx = end;
+    if(start > end)
+     return NULL;
+
+    int curr = post[idx];
+    idx--;
+    Node* node = new Node(curr);
+
+    if(start == end) 
+     return node;
+
+    int pos = search(in,start,end,curr);
+    node->right = buildTreePostIn(post,in,pos+1,end);
+    node->left = buildTreePostIn(post,in,start,pos-1);
+
+    return node;
+}
+
+// Inorder function to check if tree was built successfully!!
+void inOrder(struct Node* root){
+    if(root == NULL)
+      return;
+    inOrder(root->left);
+    cout<<root->data<<" ";
+    inOrder(root->right);
+}
+
+int main(){
+    //n=5
+    int preorder[] =  {1,2,4,3,5};
+    int inorder[] = {4,2,1,5,3}; // This order should match the output
+    int postorder[] = {4,2,5,3,1};
+    Node* t1 = buildTreePreIn(preorder,inorder,0,4);
+    Node* t2 = buildTreePostIn(postorder,inorder,0,4);
+
+     /*  Tree t
+            1
+           / \
+          2   3
+         /   /
+        4   5
+    
+    */
+   cout<<"Output Inorder : ";
+   inOrder(t2);
+   return 0;
+}
\ No newline at end of file