Optimal Python Solution for Two Sum (Interview Script)
2025-10-01
The Logic
- A brute force approach checks all pairs and wastes time.
- Use a hash map to track numbers already seen.
- For each element, check whether its complement exists.
Implementation / Diagram
Key Invariant
At any index, the hash map contains all elements seen so far and their indices.
def twoSum(nums, target):
seen = {}
for i, num in enumerate(nums):
complement = target - num
if complement in seen:
return [seen[complement], i]
seen[num] = i
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