ConstructBinaryTreeFromInorderAndPostorderTraversal106

Author: fluency03

Diff for: README.md

@@ -53,11 +53,11 @@
 | [Graph](https://github.com/fluency03/leetcode-java/blob/master/src/graph) |
 
 
-# Total: 467
+# Total: 468
 
 |   Easy  |  Medium | Hard | - |
 |:-------:|:-------:|:----:|:-:|
-|   126   |   262   |  74  | 5 |
+|   126   |   263   |  74  | 5 |
 
 
 | Question | Solution | Difficulty |
@@ -150,6 +150,7 @@
 | [103. Binary Tree Zigzag Level Order Traversal](https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/BinaryTreeZigzagLevelOrderTraversal103.java) | Medium |
 | [104. Maximum Depth of Binary Tree](https://leetcode.com/problems/maximum-depth-of-binary-tree/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/MaximumDepthOfBinaryTree104.java) | Easy |
 | [105. Construct Binary Tree from Preorder and Inorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/ConstructBinaryTreeFromPreorderAndInorderTraversal105.java) | Medium |
+| [106. Construct Binary Tree from Inorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/ConstructBinaryTreeFromInorderAndPostorderTraversal106.java) | Medium |
 | [107. Binary Tree Level Order Traversal II](https://leetcode.com/problems/binary-tree-level-order-traversal-ii/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/BinaryTreeLevelOrderTraversalII107.java) | Easy |
 | [108. Convert Sorted Array to Binary Search Tree](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/ConvertSortedArrayToBinarySearchTree108.java) | Easy |
 | [109. Convert Sorted List to Binary Search Tree](https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/ConvertSortedListToBST109.java) | Medium |

Diff for: src/ConstructBinaryTreeFromInorderAndPostorderTraversal106.java

@@ -0,0 +1,51 @@
+/**
+ * Given inorder and postorder traversal of a tree, construct the binary tree.
+ * 
+ * Note:
+ * You may assume that duplicates do not exist in the tree.
+ * 
+ * For example, given
+ * 
+ * inorder = [9,3,15,20,7]
+ * postorder = [9,15,7,20,3]
+ * Return the following binary tree:
+ * 
+ *     3
+ *    / \
+ *   9  20
+ *     /  \
+ *    15   7
+ */
+
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+
+public class ConstructBinaryTreeFromInorderAndPostorderTraversal106 {
+    public TreeNode buildTree(int[] inorder, int[] postorder) {
+        if (inorder == null || postorder == null || inorder.length == 0 || postorder.length == 0 || inorder.length != postorder.length) return null;
+        int len = inorder.length;
+        return buildTree(inorder, 0, len-1, postorder, 0, len-1);
+    }
+
+    private TreeNode buildTree(int[] inorder, int ii, int ij, int[] postorder, int pi, int pj) {
+        if (ii > ij) return null;
+        int midVal = postorder[pj];
+        TreeNode curr = new TreeNode(midVal);
+        if (pi == pj) return curr;
+        
+        int mid = ii;
+        while (inorder[mid] != midVal) mid++;
+        
+        curr.left = buildTree(inorder, ii, mid-1, postorder, pi, pi+(mid-1-ii));
+        curr.right = buildTree(inorder, mid+1, ij, postorder, pi+(mid-ii), pj-1);
+        return curr;
+    }
+
+}