M的最大可能值，不超过N，且它们之间的按位OR和XOR相等

给定整数N ，任务是找到最大的数M ，其中( M )，使得N(XOR)M等于N(OR)M，即(N ^ M)=(N | M) 。

例子：

Input: N = 5 
Output: 2 
5 ^ 4 = 1 and 5 | 4 = 5. Therefore, XOR and OR between them are not equal. 
5 ^ 3 = 6 and 5 | 3 = 7. Therefore, XOR and OR between them are not equal. 
5 ^ 2 = 7 and 5 | 2 = 7. Therefore, XOR and OR between them are equal.

Input: N = 14 
Output: 1 

方法：
要获得所需的数字M ，请从N的最低有效位(LSB)到最高有效位(MSB)遍历N的所有位。这里出现两种情况：

1. 如果N的^第i位是1，则：
   • 如果M的^第i^个比特被设置为1，则N ^ M将不等于N | M为(1 ^ 1 = 0)和(1 | 1 = 1)。
   • 如果^第i^个位被设置M的为0，则N ^ M将等于N | M为(1 ^ 0 = 1)和(1 | 0 = 1)。
   • 因此，如果N的^第i位是1，M的^第i^个比特设置为0。
2. 如果N的^第i位是0，则：
   • 如果M的^第i^个比特被设置为1，则N ^ M将等于N | M为(0 ^ 1 = 1)和(0 | 1 = 1)。
   • 如果我们M的^第i^个比特设置为0，则N ^ M将等于N | M为(0 ^ 0 = 0)和(0 | 0 = 0)。
   • 因此，如果M的^第i^个比特被设置为0或1，N ^ M将总是等于N | M。
   • 由于必须找出小于N的M的最大值，因此始终将M的^第i位设置为1 。

Illustration: 

• N = 5
• 32-bit representation of 5 = 00000000000000000000000000000101
• LSB index of 5 = 31
• MSB index of 5 = 29
• Traversing from LSB to MSB i.e. from 31 to 29:
  • For index 31, N[31] = 1. So M[31] should be set to 0.
  • For index 30, N[30] = 0. So M[30] should be set to 1.
  • For index 29, N[29] = 1. So M[29] should be set to 0.
• Thus the 32-bit representation of M is 00000000000000000000000000000010, which is equal to 2 in decimal representation.

下面是上述方法的实现：

C++

// C++ Program to implement
// the above approach
#include 
using namespace std;
  
// Function to find required
// number M
int equalXORandOR(int n)
{
    // Initialising m
    int m = 0;
  
    // Finding the index of the
    // most significant bit of N
    int MSB = (int)log2(n);
  
    // Calculating required number
    for (int i = 0; i <= MSB; i++) {
  
        if (!(n & (1 << i))) {
            m += (1 << i);
        }
    }
  
    return m;
}
  
// Driver Code
int main()
{
    int n = 14;
    cout << equalXORandOR(n);
    return 0;
}

Java

// Java program to implement
// the above approach
class GFG{
  
// Function to find required
// number M
static int equalXORandOR(int n)
{
      
    // Initialising m
    int m = 0;
  
    // Finding the index of the
    // most significant bit of N
    int MSB = (int)Math.log(n);
  
    // Calculating required number
    for(int i = 0; i <= MSB; i++)
    {
        if ((n & (1 << i)) <= 0)
        {
            m += (1 << i);
        }
    }
    return m;
}
  
// Driver Code
public static void main(String[] args)
{
    int n = 14;
      
    System.out.print(equalXORandOR(n));
}
}
  
// This code is contributed by amal kumar choubey

Python3

# Python3 program to implement 
# the above approach 
from math import log2
  
# Function to find required
# number M
def equalXORandOR(n):
  
    # Initialising m
    m = 0
  
    # Finding the index of the
    # most significant bit of N
    MSB = int(log2(n))
  
    # Calculating required number
    for i in range(MSB + 1):
        if(not(n & (1 << i))):
            m += (1 << i)
  
    return m
  
# Driver Code
n = 14
  
# Function call
print(equalXORandOR(n))
  
# This code is contributed by Shivam Singh

C#

// C# program to implement
// the above approach
using System;
  
class GFG{
  
// Function to find required
// number M
static int equalXORandOR(int n)
{
      
    // Initialising m
    int m = 0;
  
    // Finding the index of the
    // most significant bit of N
    int MSB = (int)Math.Log(n);
  
    // Calculating required number
    for(int i = 0; i <= MSB; i++)
    {
        if ((n & (1 << i)) <= 0)
        {
            m += (1 << i);
        }
    }
    return m;
}
  
// Driver Code
public static void Main(String[] args)
{
    int n = 14;
      
    Console.Write(equalXORandOR(n));
}
}
  
// This code is contributed by amal kumar choubey

输出：

1

时间复杂度： O(log ₂ N)
辅助空间： O(1)