思路：

 本題的思路與LeetCode105題：從前序與中序遍歷序列構造二叉樹的思路非常類似。只不過這裡要根據後序遍歷序列遍歷當前節點而已。

class Solution {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        return helpBuild(inorder,postorder,postorder.length - 1,0,inorder.length);
    }
    public TreeNode helpBuild(int[] in, int[] post, int postIndex, int inFrom, int inTo) {
		if(inFrom >= inTo){
			return null;
		}
		TreeNode root = new TreeNode(post[postIndex]);
		for(int i=inFrom;i<inTo;i++){
			if(in[i] == post[postIndex]){
				root.right = helpBuild(in,post,postIndex - 1,i + 1,inTo);
				root.left = helpBuild(in,post,postIndex - (inTo - i),inFrom,i);
                break;
			}
		}
		return root;
	}
}