Problem Statement​

Given an array of integers nums and an integer target, return the indices of the two numbers such that they add up to target.

Video Explanation​

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Approach​

To solve this problem, we can use a hash map to store the numbers and their indices. As we iterate through the list, we check if the complement (target - current number) exists in the hash map.

Steps:​

1. Initialize:

   • Create an empty hash map.

2. Iterate:

   • For each number in nums, calculate its complement.
   • Check if the complement exists in the hash map.
   • If it exists, return the indices.
   • Otherwise, add the current number and its index to the hash map.

3. Return:

   • If no solution is found, return an empty list.

Python Implementation​

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        num_map = {}
        for i, num in enumerate(nums):
            complement = target - num
            if complement in num_map:
                return [num_map[complement], i]
            num_map[num] = i

Time Complexity: O(n)
Space Complexity: O(n)