Construct Binary Tree from Inorder and Postorder Traversal

Given inorder and postorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

和pre & in 是一样的。

/**
 * 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) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        return inorder_postorder(inorder, 0, inorder.length - 1, postorder, 0, postorder.length - 1);
    }
    public TreeNode inorder_postorder(int[] in, int is, int ie, int[] po, int ps, int pe){
        if(ps > pe || is > ie) return null;
        TreeNode root = new TreeNode(po[pe]);
        int ind = 0;
        for(int i = is; i <= ie; i++)
            if(in[i] == root.val){
                ind = i;
                break;
        }
        int len = ind - is;
        root.left = inorder_postorder(in, is, ind - 1,po, ps, ps + len - 1);
        root.right = inorder_postorder(in, ind + 1, ie, po, ps + len, pe - 1);
        return root;
    }
}