[Leetcode] Bitwise AND of Numbers Range

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.

总结规律

10110 0101 = m

10110 0110

10110 0111

10110 1000

10110 1001

10110 1010

10110 1011 = n

发现上面数字的高位的5位是相同的，第四位是不同而，我们如何找到这高五位？下面是两种实现方法。

 

public class Solution {
    private int solution1(int m,int n){
        int bitxor = 1;
        //如果当前两个数字不相等，那么就将两个数的最低位当前最低位清零。
        while(m!=n){
            int tmp = m & bitxor;
            if(tmp != 0)
                m = m ^ bitxor;
            tmp = n & bitxor;
            if(tmp!=0)
                n = n ^ bitxor;
            bitxor = bitxor << 1;
        }
        return n;
    }
    private int solution2(int m,int n){
        int order = 0;
        while(m!=n){
            m = m >> 1;
            n = n >> 1;
            order++;
        }
        return m<<order;
    }
    public int rangeBitwiseAnd(int m, int n) {
        return solution2(m,n);
    }
}