Autocomplete Solution

Implementation considerations:

$1.$ Track current input: accumulate typed characters until '#'

$2.$ Update on '#': insert the completed sentence into trie, increment frequency

$3.$ Maintain sorted suggestions: use heap or sorted insertion

$4.$ Handle special characters: spaces are valid characters in sentences

function input(c):
    if c == '#':
        this.insert(this.currentInput)
        this.currentInput = ""
        return []
    this.currentInput += c
    node = this.findNode(this.currentInput)
    if node == null:
        return []
    return top 3 suggestions from node.suggestions

This problem is complex because it combines trie operations with ranking and stateful input handling.