Programming Example
Python Two Sum
Two Sum
Two Sum
Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.
You can return the answer in any order.
Input: nums = [2,7,11,15], target = 9 Output: [0,1] Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].
Input: nums = [3,2,4], target = 6 Output: [1,2]
Input: nums = [3,3], target = 6 Output: [0,1]
Constraints:
2 <= nums.length <= 104-109 <= nums[i] <= 109-109 <= target <= 109Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
class Solution:
def twoSum(self, nums: List[int], target: int) -> List[int]:
num_indices = {}
for i, num in enumerate(nums):
complement = target - num
if complement in num_indices:
return [num_indices[complement], i]
num_indices[num] = i
return None # if no solution is found
Input: nums = [2,7,11,15], target = 9 Output: [0,1] Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].
First read the algorithm, then study the program code line by line. After that, compare the code with the output and finally go through the explanation. This approach helps learners understand both the logic and the implementation properly.
After understanding this example, try to rewrite the same program without looking at the code. Then change some values or logic and run it again. This helps improve confidence and keeps learners engaged on the page for longer.