【leetcode】 Bitwise AND of Numbers Range

最新推荐文章于 2023-12-18 09:43:22 发布

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本文介绍了解决LeetCode上关于给定范围内所有整数的按位与问题的两种方法。第一种方法通过递归分解问题，第二种方法通过移位操作找到相同的位模式。

From： https://leetcode.com/problems/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.

Solution 1：

public class Solution {
    public int rangeBitwiseAnd(int m, int n) {
        if( m>n || m<=0 || n<=0) return 0;
        if(m == n)  return m;
        if(m == n-1)    return m&n;
        int mid = (m+n)/2;
        return  mid & rangeBitwiseAnd(m,mid-1) & rangeBitwiseAnd(mid+1,n); 
    }
}

Solution 2：

class Solution {
public:
    int rangeBitwiseAnd(int m, int n) {
        if(m == 0) return 0;
        int moveFactor = 1;
        while(m != n){
            m >>= 1;
            n >>= 1;
            moveFactor <<= 1;
        }
        return m * moveFactor;
    }
};