​LeetCode刷题实战105：从前序与中序遍历序列构造二叉树

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