Update Bits

Question

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)

Have you met this question in a real interview? Yes Example

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

return N=(10001010100)2

Thoughts

要注意i,j的位数，这里都assume为32位的整数

Solution

class Solution {
    /**
     *@param n, m: Two integer
     *@param i, j: Two bit positions
     *return: An integer
     */
    public int updateBits(int n, int m, int i, int j) {
        int mask;
        if (j < 31) {
            mask = ~((1 << (j + 1)) - (1 << i));
        } else {
            mask = (1 << i) - 1;
        }
        return (m << i) + (mask & n);
    }
}