Reverse Integer

1. Question

反转一个整数的数位（注意溢出情况）

Reverse digits of an integer.

Example1: x = 123, return 321
Example2: x = -123, return -321

2. Solution

2.1 整除取余法

 1 public class Solution {
 2     public int reverse( int x ){
 3         int m = x;
 4         long res = 0;
 5         while( m!=0 ){
 6             res = res * 10 + m % 10;
 7             m /= 10;
 8         }
 9         if( res > Integer.MAX_VALUE || res < Integer.MIN_VALUE )
10             return 0;
11         return (int)res;
12     }
13 }

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2.2 字符串方法

 1 //可以直接用String的reverse方法，但是效率低
 2 public class Solution {
 3     public int reverse( int x ){
 4         String orig = String.valueOf(Math.abs(x));
 5         StringBuilder res = new StringBuilder();
 6         if( x<0 )
 7             res.append('-');
 8         for( int i=orig.length()-1; i>=0 ; i-- )
 9             res.append( orig.charAt(i) );
10         try{
11             x = Integer.parseInt(res.toString());
12         }catch( NumberFormatException e ){
13             x = 0;
14         }
15         return x;
16     }
17 }

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3. 复杂度分析

O(n)