# Construct Binary Tree from Inorder and Postorder Traversal LeetCode Solution

Here, We see Construct Binary Tree from Inorder and Postorder Traversal LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc. with different approaches.

# List of all LeetCode Solution

## Problem Statement

Given two integer arrays inorder and postorder where inorder is the inorder traversal of a binary tree and postorder is the postorder traversal of the same tree, construct and return the binary tree.

Example 1:

Input: inorder = [9,3,15,20,7], postorder = [9,15,7,20,3]
Output: [3,9,20,null,null,15,7]

Example 2:
Input: inorder = [-1], postorder = [-1]
Output: [-1]

## Construct Binary Tree from Inorder and Postorder Traversal LeetCode Solution C++

``````class Solution {
public:
TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
unordered_map<int, int> index;
for (int i = 0; i < inorder.size(); i++) {
index[inorder[i]] = i;
}
return buildTreeHelper(inorder, postorder, 0, inorder.size() - 1, 0, postorder.size() - 1, index);
}
TreeNode* buildTreeHelper(vector<int>& inorder, vector<int>& postorder, int inorderStart, int inorderEnd, int postorderStart, int postorderEnd, unordered_map<int, int>& index) {
if (inorderStart > inorderEnd || postorderStart > postorderEnd) {
return nullptr;
}
int rootVal = postorder[postorderEnd];
TreeNode* root = new TreeNode(rootVal);
int inorderRootIndex = index[rootVal];
int leftSubtreeSize = inorderRootIndex - inorderStart;
root->left = buildTreeHelper(inorder, postorder, inorderStart, inorderRootIndex - 1, postorderStart, postorderStart + leftSubtreeSize - 1, index);
root->right = buildTreeHelper(inorder, postorder, inorderRootIndex + 1, inorderEnd, postorderStart + leftSubtreeSize, postorderEnd - 1, index);
return root;
}
};```Code language: PHP (php)```

## Construct Binary Tree from Inorder and Postorder Traversal Leetcode Solution Java

``````class Solution {
public TreeNode buildTree(int[] inorder, int[] postorder) {
return buildTree(inorder, 0, inorder.length - 1, postorder, 0, postorder.length - 1);
}
private TreeNode buildTree(int[] inorder, int inStart, int inEnd, int[] postorder, int postStart, int postEnd) {
if (inStart > inEnd || postStart > postEnd) {
return null;
}
int rootVal = postorder[postEnd];
TreeNode root = new TreeNode(rootVal);
int rootIndex = 0;
for (int i = inStart; i <= inEnd; i++) {
if (inorder[i] == rootVal) {
rootIndex = i;
break;
}
}
int leftSize = rootIndex - inStart;
int rightSize = inEnd - rootIndex;
root.left = buildTree(inorder, inStart, rootIndex - 1, postorder, postStart, postStart + leftSize - 1);
root.right = buildTree(inorder, rootIndex + 1, inEnd, postorder, postEnd - rightSize, postEnd - 1);
return root;
}
}
```Code language: PHP (php)```

## Construct Binary Tree from Inorder and Postorder Traversal Leetcode Solution JavaScript

``````var buildTree = function(inorder, postorder) {
let hash = {};
for (let i=0;i<inorder.length;i++) hash[inorder[i]] = i;
let recur = function(start, end) {
if (start > end) return null;
let val = postorder.pop();
let root = new TreeNode(val);
root.right = recur(hash[val] + 1, end);
root.left = recur(start, hash[val] - 1);
return root;
}
return recur(0, inorder.length - 1);
};```Code language: JavaScript (javascript)```

## Construct Binary Tree from Inorder and Postorder Traversal Leetcode Solution Python

``````class Solution(object):
def buildTree(self, inorder, postorder):
if not inorder:
return None
root_val = postorder.pop()
root = TreeNode(root_val)
inorder_index = inorder.index(root_val)
root.right = self.buildTree(inorder[inorder_index+1:], postorder)
root.left = self.buildTree(inorder[:inorder_index], postorder)
return root``````
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