# Python: Find all pairs in a list whose sum is equal to a target value

## Python sets: Exercise-22 with Solution

Write a Python program that finds all pairs of elements in a list whose sum is equal to a given value.

**Sample Solution:**

Python Code:

```
# Define a function 'find_pairs' that takes a list of numbers 'nums' and a target value 'target_val'.
def find_pairs(nums, target_val):
# Create a set 'nums_set' to efficiently check for the presence of numbers in the input list.
nums_set = set(nums)
# Create an empty list 'pairs' to store pairs of numbers that sum up to the target value.
pairs = []
# Iterate over the unique numbers in 'nums_set'.
for n in nums_set:
# Calculate the complement of the current number with respect to the target value.
complement = target_val - n
# Check if the complement is in the 'nums_set'.
if complement in nums_set:
# If the complement exists in the set, add a pair consisting of the current number and its complement to the 'pairs' list.
pairs.append({n, complement})
# Return the 'pairs' list containing pairs of numbers that meet the criteria.
return pairs
nums = [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
print("Original list of numbers:")
print(nums)
target_val = 35
print("Target value:",target_val)
print("Find all pairs in the said list whose sum is equal to a target value:")
print(find_pairs(nums, target_val))
nums = [1, 2, 3, 4, 5]
print("\nOriginal list of numbers:")
print(nums)
target_val = 5
print("Target value:",target_val)
print("Find all pairs in the said list whose sum is equal to a target value:")
print(find_pairs(nums, target_val))
```

Sample Output:

Original list of numbers: [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20] Target value: 35 Find all pairs in the said list whose sum is equal to a target value: [{20, 15}, {16, 19}, {17, 18}, {17, 18}, {16, 19}, {20, 15}] Original list of numbers: [1, 2, 3, 4, 5] Target value: 5 Find all pairs in the said list whose sum is equal to a target value: [{1, 4}, {2, 3}, {2, 3}, {1, 4}]

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