Bitwise AND of Numbers Range

Given a range [m, n] where 0 <= m <= n <= 2147483647, return the bitwise AND of all numbers in this range, inclusive.

For example, given the range [5, 7], you should return 4.

Credits:
Special thanks to @amrsaqr for adding this problem and creating all test cases.

Tags

Bit Manipulation

思路

• 画出0 - 15的 bits
• 发现如果从m一直AND到n,那如果某位有0的,最后这个位一定也是0
• 当m与n不相等时,就开始向右移位,直到相等
• 这中间向右移位是因为这些位最后都会为0

public class Solution {
    public int rangeBitwiseAnd(int m, int n) {

        int count = 0;
        while (m != n) {
            m >>= 1;
            n >>= 1;
            count++;
        }

        return m<<=count;
    }

}