0764EasyArrayString

Reassembling The Scrambled Code

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Trains the technique from

This is an original problem, written from a brief that listed the technique, the difficulty, the topics, the function shape and the input bounds — none of that problem's wording, examples, hints or editorials. The link is there so you can map your practice onto the standard set.

Same function shape, different story and different numbers.

A ticket code came off a faulty printer with its characters out of order, but every character was tagged with the position it belongs in.

You are given code, the scrambled string, and slots of the same length. The character code[i] belongs at position slots[i] of the restored code, with positions counted from 0.

Return the restored code.

Examples

Example 1

Input: code = "dcba", slots = [3, 2, 1, 0]
Output: "abcd"

The "d" is tagged for position 3, the "c" for position 2, the "b" for position 1 and the "a" for position 0, which spells "abcd".

Example 2

Input: code = "wxy", slots = [1, 2, 0]
Output: "ywx"

The "w" goes to position 1, the "x" to position 2 and the "y" to position 0, giving "ywx".

Example 3

Input: code = "pill", slots = [2, 3, 0, 1]
Output: "llpi"

Positions 2 and 3 take the "p" and the "i", while positions 0 and 1 take the two "l" characters, spelling "llpi".

Constraints

1 <= code.length <= 100
slots.length == code.length
0 <= slots[i] <= 99
code consists of lowercase English letters only.
The values in slots are exactly the positions 0 through code.length - 1, each used once.

The signature

The editor is preloaded with this. It matches the parent problem's shape, so a solution that works here transfers to a judge unchanged.

Python

def restore_code(code: str, slots: list[int]) -> str:

Java

public String restoreCode(String code, int[] slots)

The intended approach

Time O(n) for a code of n characters.Space O(n) for the buffer, which is the returned code.

Every position of the restored code is claimed by exactly one character, so allocate a buffer of the right length and drop `code[i]` straight into buffer position `slots[i]` on a single walk. Joining the buffer gives the answer.

Pythonentry point: restore_code

def restore_code(code, slots):
    # Time O(n), space O(n) for the returned code.
    out = [""] * len(code)
    for i in range(len(code)):
        out[slots[i]] = code[i]
    return "".join(out)

The obvious version

Build the answer position by position: for output position `target`, scan the whole `slots` list for the entry equal to `target` and take the matching character. Quadratic in the code length.

This is not filler. It was written independently of the fast solution and the two were run against thousands of random inputs to confirm they agree — which is how the answer above is known to be right. Read it when the intended approach feels like a rabbit pulled out of a hat.

Python

def bf_restore_code(code, slots):
    n = len(code)
    pieces = []
    for target in range(n):
        found = ""
        for i in range(n):
            if slots[i] == target:
                found = code[i]
                break
        pieces.append(found)
    return "".join(pieces)

How this problem was checked

Reference solution executed against 10 test cases — 10 passed
3 worked examples confirmed by running the code
0 eight-word sequences shared with the parent problem's text
Agrees with an independent brute-force implementation on random inputs
Test set proven to catch deliberately broken solutions
Reviewed by a separate quality pass
Function arity matches the parent problem's

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