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# 1. Two Sum

Given an array of integers, return **indices** of the two numbers such that they add up to a specific target.

You may assume that each input would have ***exactly*** one solution, and you may not use the *same* element twice.

**Example:**

```
Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].
```

```
# @param {Integer[]} nums
# @param {Integer} target
# @return {Integer[]}
def two_sum(nums, target)
  new_hash = {}
  
  nums.each_with_index do |val, index|
    
    left = new_hash[target - val]
    
    if left
      return [left, index]
    end
    
    new_hash[val] = index
    
  end
  
end
```