Understanding Two Sum
Given an integer array nums and an integer target, return the indices of two distinct elements whose sum equals target. Return an empty array if no pair exists. Any valid pair is accepted.
How it works
Instead of searching for two values at once, ask whether the complement of the current value has already appeared.
Store each previously seen value with its index. Check for target minus the current value before inserting, so an element cannot match itself.
Try an example
Input: nums = [2, 7, 11, 15], target = 9
Output: [0, 1]
2 + 7 = 9.
Input: nums = [3, 3], target = 6
Output: [0, 1]
Equal values at different indices form a valid pair.
Constraints
- Use each index at most once.
- Negative numbers and duplicate values are allowed.
- Visualization limit: 64 integers between −1,000,000 and 1,000,000.
Use the simulator
Change the input, then choose Visualize input. Use Next and Previous to inspect each decision, or Play to advance automatically. Compare approaches and their complexity. Choose Try yourself to write JavaScript, select My code and Visualize code to inspect its execution, or Run Tests to check results.
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