Career cup 5.1

BitManipulation.java

package Chapter5;

public class BitManipulation {
    public static int overwrite(int n, int m, int i, int j) {
	int b = j - i + 1;

	// create mask with 0s from i to j and 1s in other positions
	int mask = 1;
	while (b > 0) {
	    mask *= 2;
	    b--;
	}
	mask = ~((mask - 1) << i);

	// mask & n set i-j bits in N be 0
	// | (m << i) set i-j bits in N be the ones in M
	return mask & n | (m << i);
    }

    //print binary presentation of a positive integer
    private static void binaryRepr(int n) {
	String s = "";
	while (n > 0) {
	    s += (n % 2);
	    n /= 2;
	}
	for (int i = s.length() - 1; i >= 0; i--)
	    System.out.print(s.charAt(i));
	System.out.println();
    }

    public static void main(String[] args) {
	binaryRepr(1024);
	binaryRepr(35);
	int res = overwrite(1024, 19, 2, 6);
	binaryRepr(res);
    }
}