We use a hash map (dictionary in Python) to store the value and its index as we iterate through the array. For each number, we calculate the complement (target - current_number). If the complement is already in our map, it means we found the pair.

1. Initialize an empty dictionary seen.
2. Iterate through the array using enumerate to get both index i and value num.
3. Calculate complement = target - num.
4. Check if complement exists in seen.
5. If it exists, return [seen[complement], i].
6. Otherwise, add the current num to seen with its index: seen[num] = i.

• Time Complexity: O(N), where N is the number of elements in the array. We traverse the list only once.
• Space Complexity: O(N), as we store at most N elements in the hash map.

def solve(nums, target):
    # Dictionary to store value: index
    seen = {}
    
    for i, num in enumerate(nums):
        complement = target - num
        # If complement is found, return the indices
        if complement in seen:
            return [seen[complement], i]
        # Store index of the current number
        seen[num] = i
    
    return [] # Should not reach here based on problem constraints