Two Sum (Unsorted) in Java: Explanation & Practice

Find two numbers that add up to target using HashMap

Problem summary

Given an unsorted array and target, find two numbers that add up to target. Use HashMap for O(n) solution.

Starter code

public class Main {
    public static void main(String[] args) {
        int[] nums = {2, 7, 11, 15};
        int target = 9;
        
        // Store complement in HashMap
        // For each num, check if (target - num) exists
        // Print: Indices: 0, 1
    }
}

Expected output and test cases

[2,7,11,15], target=9
```
Indices: 0, 1
```
[3,2,4], target=6
```
Indices: 1, 2
```
[3,3], target=6
```
Indices: 0, 1
```

Hints

For each number, its complement is target - number
Store each number with its index in HashMap
Before storing, check if complement already exists
If yes, we found our pair!

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