cc150_5_3.java

public class Q5_3 {
	public static void main(String[] args){
		int test = 0b11011001111111;
		System.out.println(Integer.toBinaryString(test));
		System.out.println(Integer.toBinaryString(getPrevious(test)));
		System.out.println(Integer.toBinaryString(getNext(test)));
	}
	
	public static int getPrevious(int n){
		if(n < 0) return -1;
		int t= n;
		int trailingonecnt = 0;
		int zerocnt = 0;
		
		// Find first trailing zeros
		while(t > 0 && ((t & 1) == 1)){
			t = t >> 1;
			trailingonecnt ++;
		}
		
		if(t == 0) return -1;
		
		// Find 10 part
		while(t > 0 && ((t & 1) == 0))
		{
			t = t >> 1;
			zerocnt ++;
		}
		
		int pos = zerocnt + trailingonecnt;
		// Fill pos bit with one
		n = n & (~0 << pos+1);
//		System.out.println("inside");
//		System.out.println("pos:"+pos);
//		System.out.println(Integer.toBinaryString(n));
		// Fill 1 on the right of the pos
		int rstones = (1 << (trailingonecnt + 1)) - 1;
		n = n | (rstones << (zerocnt -1));
		
		return n;
	}

	
	public static int getNext(int n){
		if(n < 0) return -1;
		int t= n;
		int trailingonecnt = 0;
		int onecnt = 0;
		
		// Find first trailing zeros
		while(t > 0 && ((t & 1) == 0)){
			t = t >> 1;
			trailingonecnt ++;
		}
		
		if(t == 0) return -1;
		
		// Find 10 part
		while(t > 0 && ((t & 1) == 1))
		{
			t = t >> 1;
			onecnt ++;
		}
		
		int pos = onecnt + trailingonecnt;
		// Fill pos bit with 1
		n = n | (1 << pos);
		// Clear pos-1 to 0
		int allones = ~0;
		int mask = allones << (pos);
		n = n & mask;
		// Fill 1 on the right of the pos
		
		int rstones = (1 << (onecnt-1)) - 1;
		n |= rstones;
		
		return n;
	}
	
}