已知BST的前序遍历，还原BST

已知BST的前序遍历，还原BST

arr数组：前序遍历
list：排序后的 arr 数组【BST的 中序遍历】

 public static TreeNode getRoot(int[] arr, List<Integer> list){
      int index = -1;
      for (int i = 0; i < arr.length; i++) {
          if (list.contains(arr[i])){
              index = Collections.binarySearch(list, arr[i]);//  以根节点进行分割
              break;
          }
      }
      TreeNode treeNode = new TreeNode(list.get(index));
      List<Integer> left = list.subList(0, index);
      if (left.size() > 0){
          treeNode.left = getRoot(arr, left);
      }
      List<Integer> right = list.subList(index + 1, list.size());
      if (right.size() > 0){
          treeNode.right = getRoot(arr, right);
      }
      return treeNode;
  }