You are 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)

CC150-5.1.java

package POJ;

public class Main{
 
	/**
	 * 
	 * 5.1 You are 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)
	 * 
	 * EXAMPLE:
	 * Input: N = 10000000000, M = 10101, i = 2, j = 6
	 * Output: N = 10001010100
	 * 
	 * Solution:
	 * 1. clear the bits j through i in N
	 * 2. shift M so that it lines up with bits j through i
	 * 3. merge M and N
	 * 
	 */

	public int updateBits(int n, int m, int i, int j) {
		// create a mask to clear bits i through j in n
		// Example: i=2, j=4, result should be 11100011
		// for simplicity, we'll use just 8 bits for the example
		int allOnes = ~0; // will equal sequence of all 1s
		int left = allOnes << (j + 1); // left: 11100000
		int right = ((1 << i) - 1); // right:00000011
		int mask = left | right; // mask: 11100011
		// clear bits j through i then put m in there
		int n_cleared = n & mask; // clear bits j through i
		int m_shifted = m << i; // move m into correct position
		return (n_cleared | m_shifted);
	}
}