CareerCup 150

C.C 5.1

/**
 * 5.1 You are given two 32-bit numbers, N andM, and two bit positions, i and j.
 * Write a method to insert M into Nsuch that M starts at bit j and ends at bit
 * i. You can assume that the bits j through i have enough space to fit all ofM.
 * That is, ifM= 10011, you can assume that there are at least 5 bits between j
 * and i. You would not, for example, have j-3 and i=2, because M could not
 * fully fit between bit 3 and bit 2. EXAMPLE: Input: N = 10000000000, M =
 * 10011, i = 2, j = 6 Output: N = 10001001100
 *
 *
 * @author Garden
 */
public class CC5_1 {

    public static int insert(int N, int M, int i, int j) {

        //to all ones: 11111111111111111111111111111111
        int allOne = ~0;
        //all ones before j, then 0s
        int left = allOne << (j + 1);
        //all 0s before i, then 1s
        int right = ((1 << i) - 1);
        //all ones, but range i - j are 0s
        int mask = left | right;
        //clear bits through j to i
        int clear = N & mask;
        //move M to the right place
        int shift = M << i;
        //clear | shift
        return clear | shift;
    }

    public static void main(String[] args) {
        int N = 0b10000000000;
        int M = 0b10011;
        int i = 2;
        int j = 6;
        System.out.println(Integer.toBinaryString(insert(N, M, i, j)));
    }
}