Sum Without Addition

mediumcodingAlgorithmsBit Manipulation~20 min

Asked at Google, Meta

Overview

Given two integers a and b, return their sum without using the + or - operators.

Constraints

-1000 <= a, b <= 1000
Must use bitwise operations only.
JavaScript handles 32-bit integers for bitwise ops.

Examples

getSum(1, 2);
// => 3

getSum(-1, 1);
// => 0

getSum(0, 0);
// => 0

Solution

Reveal solution

function getSum(a, b) {
  while (b !== 0) {
    const carry = (a & b) << 1;
    a = a ^ b;
    b = carry;
  }
  return a;
}

XOR gives the sum without carry. AND followed by left-shift gives the carry. Repeat until there is no carry.

Resources

sum-without-addition.js

Sum Without Addition

mediumcodingAlgorithmsBit Manipulation

Overview

Given two integers a and b, return their sum without using the + or - operators.

Constraints

-1000 <= a, b <= 1000
Must use bitwise operations only.
JavaScript handles 32-bit integers for bitwise ops.

Examples

getSum(1, 2);
// => 3

getSum(-1, 1);
// => 0

getSum(0, 0);
// => 0

Solution

Reveal solution

function getSum(a, b) {
  while (b !== 0) {
    const carry = (a & b) << 1;
    a = a ^ b;
    b = carry;
  }
  return a;
}

XOR gives the sum without carry. AND followed by left-shift gives the carry. Repeat until there is no carry.

Resources

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