[Swift]LeetCode7.反转整数|ReverseInteger

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Given a 32-bit signed integer, reverse digits of an integer.

Example 1:

Input: 123
Output: 321

Example 2:

Input: -123
Output: -321

Example 3:

Input: 120
Output: 21

Note:
Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231, 231 − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

给定一个 32 位有符号整数，将整数中的数字进行反转。

示例 1:

输入: 123
输出: 321

示例 2:

输入: -123
输出: -321

示例 3:

输入: 120
输出: 21

注意:

假设我们的环境只能存储 32 位有符号整数，其数值范围是 [−231, 231 − 1]。根据这个假设，如果反转后的整数溢出，则返回 0。

12ms

 1 class Solution {
 2     func reverse(_ x: Int) -> Int {
 3         //x为常量，赋值为变量
 4         var num:Int = x
 5         var rev:Int = 0
 6          while(num != 0)
 7         {
 8             var pop:Int = num % 10
 9             num /= 10
10             if((rev > Int32.max/10)||(rev == Int32.max/10 && pop > 7)){return 0}
11             if((rev < Int32.min/10)||(rev == Int32.min/10 && pop < -8)){return 0}
12             rev = rev * 10 + pop
13         }
14         return rev
15     }
16 }

12ms

 1 class Solution {
 2     func reverse(_ x: Int) -> Int {
 3        
 4         guard x != 0  && abs(x) < INT32_MAX else{
 5             return 0
 6         }
 7         var result = 0
 8         var num = abs(x)
 9         while num > 0{
10             let cursor = num % 10
11             if cursor == 0 && result == 0{
12                 num /= 10
13                 continue
14             }else{
15                 result = result * 10 + cursor
16                 num /= 10
17             }
18         }
19         if result >= INT32_MAX{
20             return 0
21         }
22         return (x > 0) ? result : -result
23     }
24 }

16ms

 1 class Solution {
 2     func reverse(_ x: Int) -> Int {
 3         var str = String(x)
 4         var sign = ""
 5         if x < 0 {
 6           sign = String(str.remove(at: str.startIndex)) 
 7         }
 8         
 9         let result = Int("\(sign)\(String(str.reversed()))") ?? 0
10         
11         let lowerLimit = Int(pow(Double(-2), 31))
12         let higherLimit = Int(pow(Double(2), 31)-1)
13         
14         return result < lowerLimit || result > higherLimit ? 0 : result
15     }
16 }

20ms

 1 class Solution {
 2     func reverse(_ x: Int) -> Int {
 3       let str = Array(String(x))
 4         var rev : [Character] = []
 5         for i in 0..<str.count {
 6             let index = str.count-i-1
 7             if (str[index] == "-") { continue }
 8             rev.append(str[index])
 9         }
10                 
11         // if we can convert the reverse string to a 32bit Int ... else return 0
12         if let result = Int32(String(rev)) { 
13         // signum == 1 or -1 if x is negative
14             return Int(result) * x.signum() 
15         } else {
16             return 0
17         }
18 }
19 }

24ms

 1 class Solution {
 2     func reverse(_ x: Int) -> Int {
 3         let tmp = x < 0 ? -1 : 1
 4         let returnVal = Int(String(abs(x).description.reversed())) ?? 0
 5         if returnVal > Int(Int32.max) || returnVal < Int(Int32.min) {
 6             return 0
 7         }
 8         return returnVal * tmp
 9     }
10 }

28ms

 1 class Solution {
 2     func reverse(_ x: Int) -> Int {
 3         var temp: Int = x
 4         var answer: UInt = 0
 5         var isNegative: Bool = false
 6 
 7         // Flip negatiave to positive
 8         if x < 0 {
 9             isNegative = true
10             if x == Int.min {
11                 temp = (temp + 1) * -1
12                 temp += 1
13             } else {
14                 temp *= -1
15             }
16         }
17         
18         // Reverse the numbers
19         while temp > 0 {
20             // Get last digit
21             answer = (answer * 10) + (UInt(temp) % 10)
22             
23             // Remove last digit
24             temp = temp / 10
25         }
26         
27         print("answer: \(answer)")
28         print("max: \(UInt(Int.max))")
29         
30         if answer > UInt(Int32.max) {
31             return 0
32         }
33         
34         if (isNegative) {
35             return Int(answer) * -1
36         } else {
37             return Int(answer)
38         }
39     }
40 }