Solving Two Sum using Hash map.

Problem

Find two numbers that add to target.

Pattern

This problem demonstrates the Hash map pattern.

Approach

Use HashMap to store complements.

Solution 

  // Solution for Two Sum
// Pattern: Hash map
// O(n) time, O(n) space

Complexity

O(n) time, O(n) space

Best Practices

  • Identify the pattern before coding — pattern recognition saves time
  • Handle edge cases: empty input, single element, duplicates
  • Use descriptive variable names even in timed interviews
  • Test with the provided examples plus one custom case