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

public class Solution {
    public int reverse( int x ){
        int m = x;
        long res = 0;
        while( m!=0 ){
            res = res * 10 + m % 10;
            m /= 10;
        }
        if( res > Integer.MAX_VALUE || res < Integer.MIN_VALUE )
            return 0;
        return (int)res;
    }
}

2.2 字符串方法

//可以直接用String的reverse方法，但是效率低
public class Solution {
    public int reverse( int x ){
        String orig = String.valueOf(Math.abs(x));
        StringBuilder res = new StringBuilder();
        if( x<0 )
            res.append('-');
        for( int i=orig.length()-1; i>=0 ; i-- )
            res.append( orig.charAt(i) );
        try{
            x = Integer.parseInt(res.toString());
        }catch( NumberFormatException e ){
            x = 0;
        }
        return x;
    }
}

3. 复杂度分析

O(n)