3.2 KiB
3.2 KiB
7 Reverse Integer
Subject
Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range \([-2^{31}, 2^{31} - 1]\), then return 0.
Assume the environment does not allow you to store 64-bit integers (signed or unsigned).
Example 1:
Input: x = 123 Output: 321
Example 2:
Input: x = -123 Output: -321
Example 3:
Input: x = 120 Output: 21
Constraints:
-231 <= x <= 231 - 1
Solution
#lang racket#lang racket/base
(for/list ([i (in-naturals)]
#:break (> i 10))
i)| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
(define/contract (ten-power-below x)
(-> exact-integer? exact-integer?)
(let ((power-of-ten 1))
(for/list ([exponent (in-naturals)])
#:break (> power-of-ten x)
(set! power-of-ten (* 10 power-of-ten)))
(/ power-of-ten 10)))#lang racket
<<ten-power-below>>
(ten-power-below 11)10
#lang racket
<<ten-power-below>>
(ten-power-below 100)100
#lang racket
<<ten-power-below>>
(ten-power-below 1111)1000
<<ten-power-below>>
(for/list ([i (list 1 100 271091029 (- 123001))])
(ten-power-below i))| 1 | 100 | 1000000000 | 1 |
<<ten-power-below>>
(define/contract (reverse x)
(-> exact-integer? exact-integer?)
(cond ((= x 0) 0)
((< x 0) (- (reverse (- x))))
(#t (let* ((remains x)
(previous remains)
(number 0)
(power-of-ten (ten-power-below x))
(current-number-power-of-ten 1)
(digit 0))
(for/list ([i (in-naturals)]
#:break (< power-of-ten 1))
(set! previous remains)
(set! remains (modulo remains power-of-ten))
(set! digit (/ (- previous remains) power-of-ten))
(set! number (+ number (* digit current-number-power-of-ten)))
(set! power-of-ten (/ power-of-ten 10))
(set! current-number-power-of-ten (* current-number-power-of-ten 10))
)
number))))#lang racket
<<reverse>>
(reverse 123)321
#lang racket
<<reverse>>
(reverse 21)12
#lang racket
<<reverse>>
(reverse -1)-1
#lang racket
<<reverse>>
(reverse -124)-421
#lang racket
<<reverse>>
(reverse 123456789012345678901234567890)98765432109876543210987654321
#lang racket
<<reverse>>
(reverse 10)1