第106题：从中序与后序遍历序列构造二叉树

class Solution {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        if(postorder.length>0) {
             TreeNode root =new TreeNode(postorder[postorder.length-1]);
             List<Integer> order=new ArrayList<Integer>();
             for(int i=0;i<inorder.length;i++) {
                 order.add(inorder[i]);
             }
             getTree(postorder,postorder.length-1,order,root);         
             return root;
         } else {
             return null;
         }
    }
      public void getTree(int[]postorder ,int number,List<Integer> order,TreeNode root) {
        if(order.size()==1) {
            return ;
        }
        
        int ordernum=order.indexOf(postorder[number]);
        if(ordernum>0) {
        List<Integer> leftOrder=new ArrayList<Integer>(order.subList(0, ordernum));        
        for(int i=number-1;i>=0;i--)
        {
            if(leftOrder.contains(postorder[i])) {
                root.left=new TreeNode(postorder[i]);
                getTree(postorder,i,leftOrder,root.left);
                break;
            }
            
         }
        }
        
        if(ordernum<order.size()-1)
        {
            List<Integer> rightOrder=new ArrayList<Integer>(order.subList(ordernum+1, order.size()));
            for(int j=number-1;j>=0;j--) {
                if(rightOrder.contains(postorder[j])) {
                    root.right=new TreeNode(postorder[j]);
                    getTree(postorder,j,rightOrder,root.right);
                    break;
                }
            }
        }
       
    }
}