Update Bits

Description:

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

Given N=(10000000000)2, M=(10101)2, i=2, j=6
return N=(10001010100)2

Note

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

Challenge

Minimum number of operations?

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.

Solution:

class Solution {
public:
	/**
	 *@param n, m: Two integer
	 *@param i, j: Two bit positions
	 *return: An integer
	*/
	int updateBits(int n, int m, int i, int j) {
		return n & ~((j == 31 ? 0xffffffff : (1<<j+1)-1) - (1<<i)+1) | m<<i;
	}
};

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Steps:

(e.g. n = (100,0000,0000)2, m = (1,0101)2, i = 2, j = 6)

1. (1<<j+1) - (1<<i) : 0000,0000,0000,0000,0000,0000,0111,1100
2. ~((1<<j+1) - (1<<i)) : 1111,1111,1111,1111,1111,1111,1000,0011
3. n & ~((1<<j+1) - (1<<i)) : 0000,0000,0000,0000,0000,0100,0000,0000
4. m<<i : 101,0100
5. n & ~((1<<j+1) - (1<<i)) | m<<i : 0000,0000,0000,0000,0000,0100,0101,0100

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