From 2ba538c9658dfc1048f28f9459f4719f982abdf3 Mon Sep 17 00:00:00 2001
From: PrakarshKamal <kamalp@mcmaster.ca>
Date: Thu, 26 Feb 2026 14:10:55 -0500
Subject: [PATCH] Complete Trees-2

---
 ConstructBTFromPostAndIn.java | 46 +++++++++++++++++++++++++++++++++++
 SumRootToLeaf.java            | 33 +++++++++++++++++++++++++
 2 files changed, 79 insertions(+)
 create mode 100644 ConstructBTFromPostAndIn.java
 create mode 100644 SumRootToLeaf.java

diff --git a/ConstructBTFromPostAndIn.java b/ConstructBTFromPostAndIn.java
new file mode 100644
index 00000000..1fefe0a1
--- /dev/null
+++ b/ConstructBTFromPostAndIn.java
@@ -0,0 +1,46 @@
+import java.util.*;
+
+// Recursion, O(n) time, O(h) space
+class Solution {
+    private int postIndex;
+
+    public TreeNode buildTree(int[] postorder, int[] inorder) {
+        postIndex = postorder.length-1;
+        Map<Integer, Integer> map = new HashMap<>();
+
+        for (int i = 0; i < inorder.length; i++) {
+            map.put(inorder[i], i);
+        }
+
+        return helper(postorder, 0, inorder.length-1, map);
+    }
+
+    private TreeNode helper(int[] postorder, int start, int end, Map<Integer, Integer> map) {
+        if (start > end) return null;
+
+        TreeNode root = new TreeNode(postorder[postIndex]);
+        postIndex--;
+
+        int mid = map.get(root.val);
+        
+        root.right = helper(postorder, mid+1, end, map);
+        root.left = helper(postorder, start, mid-1, map);
+
+        return root;
+    }
+}
+
+
+class TreeNode {
+    int val;
+    TreeNode left;
+    TreeNode right;
+    TreeNode() {}
+    TreeNode(int val) { this.val = val; }
+    TreeNode(int val, TreeNode left, TreeNode right) {
+        this.val = val;
+        this.left = left;
+        this.right = right;
+    }
+}
+ 
\ No newline at end of file
diff --git a/SumRootToLeaf.java b/SumRootToLeaf.java
new file mode 100644
index 00000000..e5bbfa1f
--- /dev/null
+++ b/SumRootToLeaf.java
@@ -0,0 +1,33 @@
+// O(n) time, O(n) space
+class Solution {
+    public int sumNumbers(TreeNode root) {
+        return helper(root, 0);
+    }
+
+    private int helper(TreeNode root, int currSum) {
+        if (root == null) return 0;
+
+        currSum = currSum * 10 + root.val;
+
+        if (root.left == null && root.right == null) {
+            return currSum;
+        }
+        int left = helper(root.left, currSum);
+        int right = helper(root.right, currSum);
+
+        return left + right;
+    }
+}
+
+class TreeNode {
+    int val;
+    TreeNode left;
+    TreeNode right;
+    TreeNode() {}
+    TreeNode(int val) { this.val = val; }
+    TreeNode(int val, TreeNode left, TreeNode right) {
+        this.val = val;
+        this.left = left;
+        this.right = right;
+    }
+}
\ No newline at end of file