comefrom: <doocs>0099.Recover Binary Search Tree_1.py
code: def dfs(root):
      nonlocal prev, first, second
      if root:
          dfs(root.left)
          if prev:
              if first is None and root.val < prev.val:
                  first = prev
              if first and root.val < prev.val:
                  second = root
          prev = root
          dfs(root.right)
masked: def sample_funcname ( var_1 ) :
      nonlocal var_2 , var_3 , var_4
      if var_1 :
          var_0 ( var_1.left )
          if var_2 :
              if var_3 is None and var_1.val < var_2.val :
                  var_3 = var_2
              if var_3 and var_1.val < var_2.val :
                  var_4 = var_1
          var_2 = var_1
          var_0 ( var_1.right )
  