Update Bits

Given two 32-bit numbers, N and M, and two bit positions, i and j. Write a method to set all bits between i and j in N equal to M (e g , M becomes a substring of N located at i and starting at j)

In the function, the numbers N and M will given in decimal, you should also return a decimal number.

Clarification:

You can assume that the bits j through i have enough space to fit all of M. That is, if M=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:

Given N=(10000000000)2, M=(10101)2, i=2, j=6

return N=(10001010100)2

Solution:

• Shift m to left with i.
• Create a mask x that only has one between i and j.
• Use xor between n and (x & n) to remove the old bits between i and j in n.
• Perform or between m and result from previous step.

Code:

class Solution {

    public int updateBits(int n, int m, int i, int j) {
        // write your code here
        int x = 0;
        m = m << i;
        for (; i <= j; i++) {
            x += 1 << i;
        }
        return n ^ (x & n) | m;
    }
}