【leetcode】Construct Binary Tree from Inorder and Postorder Traversal

        5

      /   
    2      4

  /   \      
1      3       6

 1 /**
 2  * Definition for binary tree
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     public int InorderIndex(int[] inorder,int key){
12         if(inorder == null || inorder.length == 0)
13             return -1;
14         
15         for(int i = 0;i < inorder.length;i++)
16             if(inorder[i] == key)
17                 return i;
18         
19         return -1;
20     }
21     public TreeNode buildTreeRec(int[] inorder,int[] postorder,int instart,int inend,int postart,int poend){
22         if(instart > inend)
23             return null;
24         TreeNode root = new TreeNode(postorder[poend]);
25         int index = InorderIndex(inorder, root.val);
26         root.left = buildTreeRec(inorder, postorder, instart, index-1, postart, postart+index-instart-1);
27         root.right = buildTreeRec(inorder, postorder, index+1, inend, postart+index-instart, poend-1);
28         
29         return root;
30     }
31     public TreeNode buildTree(int[] inorder, int[] postorder) {
32         return buildTreeRec(inorder, postorder, 0, inorder.length-1, 0, postorder.length-1);
33     }
34 }