LeetCode 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.
题意：中序和后序建树。
思路：还是简单的递归构造。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    private TreeNode build(int[] inorder, int[] postorder, int l, int r, int len) {
		if (len <= 0) return null;
		
		int rootVal = postorder[r+len-1];
		TreeNode root = new TreeNode(rootVal);
		int index = 0;
		for (int i = 0; i < len; i++) 
			if (inorder[l+i] == rootVal) {
				index = i;
				break;
			}
		
		root.left = build(inorder, postorder, l, r, index);
		root.right = build(inorder, postorder, l+index+1, r+index, len-1-index);
		return root;
	}
	
    public TreeNode buildTree(int[] inorder, int[] postorder) {
    	return build(inorder, postorder, 0, 0, inorder.length);
    }
}