ConstructBinaryTreefromInorderandPostorderTraversal

Change-Id: I8f6f38cc196de426c64029e825e1fe93c7f88722

Author: applewjg

ConstructBinaryTreefromInorderandPostorderTraversal.java

@@ -0,0 +1,45 @@
+/*
+ Author:     Andy, [email protected]
+ Date:       Jan 16, 2015
+ Problem:    Construct Binary Tree from Inorder and Postorder Traversal
+ Difficulty: Easy
+ Source:     http://leetcode.com/onlinejudge#question_106
+ Notes:
+ Given inorder and postorder traversal of a tree, construct the binary tree.
+ Note:
+ You may assume that duplicates do not exist in the tree.
+
+ Solution: Recursion.
+ */
+/**
+ * Definition for binary tree
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+public class Solution {
+    public TreeNode buildTree(int[] inorder, int[] postorder) {
+        if(inorder.length==0||postorder.length==0||inorder.length!=postorder.length)
+            return null;
+        return buildTreeRe(inorder,0,inorder.length-1,postorder,0,postorder.length-1); 
+    }
+    public TreeNode buildTreeRe(int[] inorder,int s1,int e1, int[] postorder, int s2,int e2){
+        if(e2<s2) return null;
+        if(s2==e2) return new TreeNode(postorder[e2]);
+        int j=-1;
+        for(int i=s1;i<=e1;i++){
+            if(inorder[i]==postorder[e2]){
+                j=i;
+                break;
+            }
+        }
+        int left_len = j-s1;
+        TreeNode root = new TreeNode(postorder[e2]);
+        root.left = buildTreeRe(inorder,s1,j-1,postorder,s2,s2+left_len-1);
+        root.right = buildTreeRe(inorder,j+1,e1,postorder,s2+left_len,e2-1);
+        return root;
+    }
+}