What is wrong with my solution?(hackerrank exercise – bitwise operation)

April 15, 2022

the link for the excersize
In short, ‘n’ is series of number from 1 to n, and ‘k’ is a number.
I need to return the largest result of a&b (a<b) as long as it’s smaller than k, for example 1&2, 1&3 …2&3,2&4…

I get 0 whenever I run this function:

function getMaxLessThanK(n,k){ 
let maxPV = 0; 
for(let a=1;a<n;a++){ 
  for(let b=a+1;b<=n;b++){ 
   if(a&b<k && a&b>maxPV){ maxPV=(a&b) } 
   } 
  } 
return maxPV

}

>Solution :

It’s an operator precedence problem.

Comparison operators (<, >, …) have higher precedence than bitwise AND (&), so you need to use parentheses to group:

if ((a & b) < k && (a & b) > maxPV) {
    // ...
}

Complete snippet:

function getMaxLessThanK(n, k) {
  let maxPV = 0;
  for (let a = 1; a < n; a++) {
    for (let b = a + 1; b <= n; b++) {
      if ((a & b) < k && (a & b) > maxPV) {
        maxPV = (a & b);
      }
    }
  }
  return maxPV;
}

console.log(getMaxLessThanK(8, 5));