Reverse digits of an integer. @leetcode

ReverseInteger.java

package leetcode.simpleCoding;

/**
 * @author jeffwan
 * @date Feb 8, 2014
 * 
 * Objective: write the simple and readable codes
 * There's no algorithm in this kind of problem but some tiny simple method. Our goal is to make it as clear as possible. 
 * In addition, It's a good opportunity communicatting with interviewer about the overflow, 100 -- 001 (display). 
 * 
 * It's better to throw exception but not return -1 (Ambiguity)
 */
public class ReverseInteger {
	public static void main(String args[]) {
//		System.out.println(reverse3(1000000003)); overflow
		System.out.println(reverse(1000000003));
//		System.out.println(Integer.MAX_VALUE);
//		System.out.println(Integer.MIN_VALUE);
	}
	
	/**
	 * Actually, we don't need to concern if a number if positive or not. It will always take the operator during operation.
	 * If we don't care overflow problem, this solution will be very short.  
	 */
	
	public static int reverse(int x) {
		int result = 0;
		int originalX = x;
		while (x != 0) {
			result = result * 10 + x % 10;
			x = x /10;
		}
		
		if ((originalX > 0 && result < 0) || (originalX < 0 && result > 0)) {
			return -1;

		}
		return result;
	}
	
	
	/**
	 * Use mod to get every number and then reverse
	 * Just use int without judging x == 0 
	 */
	public static int reverse2(int x) {
		
		boolean isNegative = x < 0 ? true: false;
		x = Math.abs(x);
		int result = 0;
		while (x > 0) {
			 result = result * 10 + x % 10;
			 x = x / 10; 
		}
		if (result < 0) {  // no multioverflow?
			return -1;
		}
 		
		if (isNegative) {
			return -result; 
		}
		return result;
	}
	
	
	/**
	 * Convert integer to string, use charAt changing brutely
	 * Here I rely on function Integer.valueOf to solve the problem 100 --> 1 but not 001
	 * Didn't sovle overflow problem -- but leetcode online judge accepted? can't believe
	 * Overflow will remains in Integer.valueOf() which troughs exception that we can't handle like reverse2()
	 */
	public static int reverse3(int x) {
		if (x == 0) return 0;
		
		boolean isPositive = true;
		if (x < 0) {
			isPositive = false;
		}
		String str = Math.abs(x) + "";
		StringBuffer sb = new StringBuffer();
		
		for (int i = str.length() - 1; i >= 0; i--) {
			sb.append(str.charAt(i));
		}
		
		int result = Integer.valueOf(sb.toString());
		if(isPositive) {
			return result;  
		} else {
			return -result;
		}
	}
}