fix(findpairs) add more info and make it harder

subjects/findpairs/README.md

@@ -1,4 +1,4 @@
-## Find Pairs with Sum
+## Find Pairs
 
 ### Instructions
 
@@ -6,16 +6,18 @@ Write a program that finds all pairs of elements in an integer array that sum up
 
 In this exercise you must take in consideration the following:
 
-- Ensure its possible to have positive or negative integers in the array
-- Ensure each element is used only once in a pair
-- Allow for multiple pairs to sum up to the target value
-- Return the message "No pairs found." when no pair is present
-- Return the message "Invalid target sum." if the target is invalid
-- Return the message "Invalid number." if the number in the array is invalid
+- Ensure it's possible to have positive or negative integers in the array.
+- Ensure each element is used only once in a pair, although the element can be repeated in different pairs.
+- Allow for multiple pairs to sum up to the target value.
+- The output messages should follow the one given in the examples bellow.
+- Return the message **"No pairs found."** when no pair is present.
+- Return the message **"Invalid target sum."** if the target is invalid.
+- Return the message **"Invalid number: <number>"** if the number in the array is invalid.
+- For any input format that deviates from the specified format `"[1, 2, 3, 4, 5]" "6"`, the program will return an "Invalid input." error message.
 
 Let's consider the input `arr = [1, 2, 3, 4, 5]` and the target sum `targetSum = 6`. When we run the program, the `findPairs()` function will search for pairs in the array that sum up to `targetSum`.
 
-The expected output for this input will be:
+Here is some example of outputs:
 
 ```console
 $ go run . "[1, 2, 3, 4, 5]" "6"
@@ -24,9 +26,15 @@ $ go run . "[-1, 2, -3, 4, -5]" "1"
 Pairs with sum 1: [[0 1] [2 3]]
 $ go run . "[1, 2, 3, 4, 5]" "10"
 No pairs found.
+$ go run . "[-1, -2, -3, -4, -5]" "-5"
+Pairs with sum -5: [[0 3] [1 2]]
 $ go run . "[1, 2, 3, 4, 20, -4, 5]" "2 5"
 Invalid target sum.
 $ go run . "[1, 2, 3, 4, 20, p, 5]" "5"
 Invalid number: p
+$ go run . "[1, 2, 3, 4" "5"
+Invalid input.
+$ go run . "1, 2, 3, 4" "5"
+Invalid input.
 $
 ```