#149 Medium Time O(1) Space O(1) Animated

Sum of Two Integers

Add two integers without using + or -.

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1 Predict
2 Trace
3 Explain
4 Implement

Pattern Bitwise state reduction

Use a bit operation to retain only the information the problem needs while discarding the rest.

Approach: Bitwise Add & Carry

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Core Insight

Use a bit operation to retain only the information the problem needs while discarding the rest.

Common Pitfall

Parenthesize shifts and masks, especially when mixing comparison or arithmetic operators.

Description

Add two integers without using + or -.

Constraints

Time Complexity: O(1)
Space Complexity: O(1)

Solution — Bitwise Add & Carry

TimeO(1) SpaceO(1)

Implementation Plan

Translate the invariant into these small, testable moves.

Choose the bitwise identity.
Initialize the accumulator or mask.
Apply the operation per value or bit.
Interpret the resulting bits.

def getSum(a, b):
    mask = 0xffffffff
    
    while (b & mask) > 0:
        carry = (a & b) << 1
        a = (a ^ b)
        b = carry
        
    return (a & mask) if b > 0 else a

Missing Number

Reverse Integer

Sum of Two Integers

Steps

Description

Constraints

Tags

Solution — Bitwise Add & Carry