From 775e7b7bc264c48e3c05709fce6597d4189a8600 Mon Sep 17 00:00:00 2001
From: dewann <dewanidhi@gmail.com>
Date: Sun, 8 Feb 2026 10:28:13 -0800
Subject: [PATCH 1/2] Implement root-to-leaf sum calculation

---
 rootToLeafSum | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)
 create mode 100644 rootToLeafSum

diff --git a/rootToLeafSum b/rootToLeafSum
new file mode 100644
index 00000000..d4157d53
--- /dev/null
+++ b/rootToLeafSum
@@ -0,0 +1,34 @@
+//TC :- O(n)
+ //SC:- O(h)
+
+ 
+class Solution {
+    int xsum = 0;
+
+    public int sumNumbers(TreeNode root) {
+        if (root == null)
+            return xsum;
+        helper(root, 0);
+        return xsum;
+
+    }
+
+    private void helper(TreeNode root, int sum) {
+        if (root == null) {
+          
+            return;
+        }
+        sum=10 * sum + root.val;
+        if (root.left == null && root.right == null) {
+            
+            xsum = xsum + sum;
+        }
+      
+        helper(root.left, sum);
+
+       
+        helper(root.right, sum);
+
+      
+    }
+}

From 57f7814362a7a93ab8ab78f1f864cd2f33b97b20 Mon Sep 17 00:00:00 2001
From: dewann <dewanidhi@gmail.com>
Date: Sun, 8 Feb 2026 10:31:21 -0800
Subject: [PATCH 2/2] Implement binary tree construction from inorder and
 postorder

---
 BTinorderPostorder | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100644 BTinorderPostorder

diff --git a/BTinorderPostorder b/BTinorderPostorder
new file mode 100644
index 00000000..b1652799
--- /dev/null
+++ b/BTinorderPostorder
@@ -0,0 +1,31 @@
+//O(n) TC
+// O(n) SC
+class Solution {
+     HashMap<Integer,Integer> hm ;
+        int postIdx;
+    public TreeNode buildTree(int[] inorder, int[] postorder) {
+        this.hm=new HashMap();
+        postIdx=postorder.length-1;
+        for(int i=0;i<postorder.length;i++){
+            hm.put(inorder[i],i);
+        }
+
+       return helper(postorder,0,postorder.length-1);
+        
+    }
+    private TreeNode helper(int[] postorder,int st,int end){
+        if(st>end) return null;
+        
+         int rootVal=postorder[postIdx];
+        int rootIdx=hm.get(rootVal);
+       
+        postIdx--;
+
+        TreeNode root=new TreeNode(rootVal);
+        root.right=helper(postorder,rootIdx+1,end);
+        root.left=helper(postorder,st,rootIdx-1);
+        return root;
+
+       
+    }
+}