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1. Sum of List Elements2. Largest Element in List3. Smallest Element in List4. Count Occurrences in List5. Remove Duplicates from List6. Merge Two Lists7. Intersection of Lists8. Union of Lists9. Sort List10. Reverse List11. Check if List is Sorted12. Find Second Largest Element13. Find N Largest Elements14. Clone / Copy List15. Rotate List16. Remove Empty Lists17. Flatten Nested List18. Find Common Elements of Two Lists19. List Slicing Programs20. Replace List Elements21. Remove Element by Value22. Count Prime Numbers in List23. Pair Sum Problem24. Unique Elements from Both Lists25. List Difference

Pair Sum Problem in Python

Check if there exists a pair of numbers in the list that adds up to a target sum.

IntermediateList ProgramsExample 23 of 25
pair-sum-problem.py
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1# Program to check if any pair in list sums to target
2

3numbers = list(map(int, input("Enter integers separated by space: ").split()))
4target = int(input("Enter target sum: "))
5

6seen = set()
7found = False
8

9for x in numbers:
10    if target - x in seen:
11        found = True
12        break
13    seen.add(x)
14

15if found:
16    print("Found a pair with the given sum.")
17else:
18    print("No pair with the given sum found.")

Output

Enter integers separated by space: 1 2 3 4
Enter target sum: 5
Found a pair with the given sum.

What's going on

We use a set to track seen numbers and check for the complement (target - x) in O(1) average time.

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