Python: Find a pair of elements from a given array whose sum equals a specific target number

Last update on July 09 2025 10:44:24 (UTC/GMT +8 hours)

5. Find a Pair of Elements Whose Sum Equals a Specific Target

Write a Python class to find a pair of elements (indices of the two numbers) from a given array whose sum equals a specific target number.

Difficulty: Medium. Company: Google, Facebook

Sample Solution-1:

Python Code:

class py_solution:
  def twoSum(self, nums, target):
       lookup = {}
       for i, num in enumerate(nums):
           if target - num in lookup:
               return (lookup[target - num], i )
           lookup[num] = i
print("index1=%d, index2=%d" % py_solution().twoSum((10,20,10,40,50,60,70),50))

Sample Output:

index1=2, index2=3 

Pictorial Presentation:

Flowchart:

Sample Solution-2:

Python Code:

class py_solution(object):
   def twoSum(self, nums, target_num):      
       """
       :type nums: list[int]
      :type target: int
      :return type: list[int]
      """
       result_dict = dict()
       pos = 0
       while pos < len(nums):
           if (target_num - nums[pos]) not in result_dict:
               result_dict[nums[pos]] = pos
               pos += 1
           else:
               return [result_dict[target_num - nums[pos]], pos]
print(py_solution().twoSum([10,20,10,40,50,60,70],50))
print(py_solution().twoSum([10,20,10,40,50,60,70],52))

Sample Output:

[2, 3]
None

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Python class that uses the two-sum algorithm with a dictionary to find two indices such that the corresponding elements add up to a target value.
• Write a Python class that implements the two-pointer technique on a sorted array to find a pair with a given sum, returning their indices.
• Write a Python class that employs recursion to search for a pair of numbers in an unsorted array that sum to a target, ensuring each element is used only once.
• Write a Python class that handles multiple possible pairs by returning the first valid pair found that meets the target sum condition.

Go to:

• Python Class Exercises Home ↩
• Python Exercises Home ↩

Previous: Write a Python class to get all possible unique subsets from a set of distinct integers.
Next: Write a Python class to find the three elements that sum to zero from a set (array) of n real numbers.

Python Code Editor:

Contribute your code and comments through Disqus.