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I have a list of numbers like [1, 2, 2, 3, 3, 2, 3, 3, 4] which I need to convert into a tree, like below:

             1
          /  |  \
         2   2   2
            / \  / \
           3   3 3  3
                    \
                     4

Note: within the list, each number cannot be +2 or more than +2 compared to the preceding value.

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  • Hi Ajay, welcome to StackOverflow. Could you include code that you have tried so far? Commented Dec 17, 2019 at 18:10

1 Answer 1

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This can be done in a natural way, using a stack of nodes:

  • Initialise an empty stack.
  • For each number x in the list:
    • Create a node node with value x.
    • Pop until either the stack is empty, or the top node in the stack has value x - 1.
    • If the stack is non-empty, add an edge from node to the node at the top of the stack.
    • Push node to the stack.
  • Return the node at the bottom of the stack; this is the root node.
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