Merge pull request #2047 from Lozakaka/patch-4

Update 0106.从中序与后序遍历序列构造二叉树.md

problems/0106.从中序与后序遍历序列构造二叉树.md

@@ -622,7 +622,42 @@ class Solution {
     }
 }
 ```
+```java
+class Solution {
+    public TreeNode buildTree(int[] inorder, int[] postorder) {
+        if(postorder.length == 0 || inorder.length == 0)
+            return null;
+        return buildHelper(inorder, 0, inorder.length, postorder, 0, postorder.length);
     
+    }
+    private TreeNode buildHelper(int[] inorder, int inorderStart, int inorderEnd, int[] postorder, int postorderStart, int postorderEnd){
+        if(postorderStart == postorderEnd)
+            return null;
+        int rootVal = postorder[postorderEnd - 1];
+        TreeNode root = new TreeNode(rootVal);
+        int middleIndex;
+        for (middleIndex = inorderStart; middleIndex < inorderEnd; middleIndex++){
+            if(inorder[middleIndex] == rootVal)
+                break;
+        }
+
+        int leftInorderStart = inorderStart; 
+        int leftInorderEnd = middleIndex;
+        int rightInorderStart = middleIndex + 1;
+        int rightInorderEnd = inorderEnd;
+
+
+        int leftPostorderStart = postorderStart;
+        int leftPostorderEnd = postorderStart + (middleIndex - inorderStart);
+        int rightPostorderStart = leftPostorderEnd;
+        int rightPostorderEnd = postorderEnd - 1;
+        root.left = buildHelper(inorder, leftInorderStart, leftInorderEnd,  postorder, leftPostorderStart, leftPostorderEnd);
+        root.right = buildHelper(inorder, rightInorderStart, rightInorderEnd, postorder, rightPostorderStart, rightPostorderEnd);
+
+        return root;
+    }  
+}
+```
 105.从前序与中序遍历序列构造二叉树
 
 ```java