1839. Swap Place and Digit
A teacher writes a number whose digits are a shuffle of 1 up to the number of digits, such as 21453. Number the places from the right starting at 1. In 21453 the digit 3 sits in place 1, the digit 5 in place 2, the digit 4 in place 3, the digit 1 in place 4 and the digit 2 in place 5.
The inverse swaps the roles of place and digit: wherever the digit x sat in place i, the inverse has the digit i in place x. For 21453 that gives 23154. Given n, return its inverse. The digits of n are always a permutation of 1 to d, where d is the number of digits. Aim for O(d) time and O(1) extra space.
Example 1
- Input:
- n = 21453
- Output:
- 23154
- Explanation:
Each digit x in place i becomes the digit i in place x, which gives 23154.
Example 2
- Input:
- n = 21
- Output:
- 21
- Explanation:
Swapping place and digit gives 21 again.
Example 3
- Input:
- n = 3412
- Output:
- 3412
- Explanation:
This number happens to be its own inverse.
Constraints
1 ≤ n ≤ 987654321
the digits of n are a permutation of 1, 2, ..., d where d is the number of digits
How this problem is judged
- Answers
- Your answer must match exactly. Numbers compare by value, so 2 and 2.0 are equal.
Expected complexity
- Time
- O(d)
- Space
- O(1)