## Convert Leveled Rich-Text Tokens into Nested Lists ### Problem Implement `read_rich_text(tokens)`. Each token is a pair `(level, text)` in document order, where `level` is a positive integer. Return a nested list that represents the levels. The outer result is the container for level 1. Before appending a token's text: - If its level is shallower than the current level, return to the existing ancestor container. - If its level is deeper, append one new child list for every missing level and descend through that chain. - Append the text to the container for its level. The input is guaranteed to be empty or to begin at level 1. Text values remain strings in the output. ### Examples ```text tokens = [(1, "food"), (4, "banana")] result = ["food", [[["banana"]]]] ``` ```text tokens = [(1, "a"), (2, "b"), (2, "c"), (1, "d")] result = ["a", ["b", "c"], "d"] ``` ```text tokens = [] result = [] ``` ### Requirements - Preserve token order. - Create exactly one list node per level transition that must be represented. - Do not mutate the input. - Explain the time and auxiliary-space complexity in terms of the number of tokens and created nesting levels. ```hint Trace level changes Work through consecutive tokens whose levels rise by three, stay equal, and then fall; note which existing output container receives each text value. ``` ### Discussion Prompts 1. What invariant connects stack length to the current token level? 2. How does the algorithm handle a jump directly from level 1 to level 4? 3. What validation would you add if the first token or a later level could be invalid?