Sum of Power of Twos and Lookup Table CodeSignal question https://codesignal.com/blog/interview-prep/example-codesignal-questions/

sumPowerTwo.js

const countSumPowerTwo = arr => {
  let result = 0;
  const hash = {};
  
  // Iterate each number in the array.
  for (let i=0; i<arr.length; i++) {
    const element = arr[i];
    const powerOfTwos = [];
    
    // Increment the count for the occurrence of this element.
    hash[element] = hash[element] ? hash[element] + 1 : 1;
    
    // Calculate the remainder from each power of two from this element.
    for (let j=0; j<21; j++) {
      const powerOfTwo = 1 << j;
      const remainder = powerOfTwo - element;
  
      // Add the count of all occurrences of this remainder.
      result += hash[remainder] ? hash[remainder] : 0;
    }
  }

  return result;
}

console.log(countSumPowerTwo([1, -1, 2, 3]));
console.log(countSumPowerTwo([2]));
console.log(countSumPowerTwo([-2, -1, 0, 1, 2]));