Career cup 5.3

FindNumber.java

package Chapter5;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class FindNumber {
    public static int findNext(int n) {
	if (n <= 0)
	    return -1;
	int t = n;
	int trailingZeroCount = 0;
	int onesCount = 0;

	// find first trailing 1 if any
	while (t > 0 && (t & 1) == 0) {
	    t = t >> 1;
	    trailingZeroCount++;
	}

	// find right most non-trailing 0
	while (t > 0 && (t & 1) == 1) {
	    t = t >> 1;
	    onesCount++;
	}

	int pos = trailingZeroCount + onesCount;
	if (pos == 31 || pos == 0)
	    return -1;

	// flip right most non-trailing 0 to 1
	n = n | (1 << pos);

	// set bits left to pos be 0
	n = n & (~((1 << pos) - 1));

	// set the right most (oneCount - 1) bits to 1
	n = n | ((1 << (onesCount - 1)) - 1);

	return n;
    }

    public static int findPrev(int n) {
	if (n <= 0)
	    return -1;
	int t = n;
	int trailingOneCount = 0;
	int zeroCount = 0;
	// find first trailing 0 if any
	while (t > 0 && ((t & 1) == 1)) {
	    t = t >> 1;
	    trailingOneCount++;
	}

	if (t==0)
	    return -1;
	
	// find the right most no trailing 1
	while (t > 0 && ((t & 1) == 0)) {
	    t = t >> 1;
	    zeroCount++;
	}

	int pos = trailingOneCount + zeroCount;

	// flip the pos from 1 to 0;
	n = n & (~(1 << pos));

	// set all bits right to pos to 0
	n = n & (~((1 << pos) - 1));

	// set 1s right to the pos
	int resetOnes = (1 << (trailingOneCount + 1)) - 1;
	n = n | (resetOnes << (zeroCount - 1));

	return n;
    }

    public static void main(String[] args) {
	System.out.print("please input a Integer: ");
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	int num = -1;
	try {
	    num = Integer.parseInt(br.readLine());
	} catch (IOException ex) {
	    System.out.println("IO error trying to read your name!");
	    System.exit(1);
	}

	System.out.println("Prev number is  " +  findPrev(num));
	System.out.println("Next number is  " +  findNext(num));
    }
}