Find all the unique pairs whose sum will be equal to a given sum

user_8007388 0
Viewed 2211

I want to find all the unique pairs whose sum will be equal to a given sum. I implement a solution but it returns only the first pair that it finds. 

func checkPairs(in numbers: [Int], forSum target: Int) -> String {    
    for (i, x) in numbers.enumerated() {
        for y in numbers[i+1 ..< numbers.count] {
            if x + y == target {
                return ("There is a pair that sums \(target): \(x)+\(y)=\(target)")
            }
        }
    }
    return "no pair"
}

print (checkPairs(in: [1, 2, 4, 4, 7, 5, 3], forSum: 8))

Output:

There is a pair that sums 8: 1+7=8
swift sorting arrays
2 Answers

You exit the function early by calling return when the first pair is found. Instead, you should return an array of tuples containing the pairs, iterate over all pairs and add the ones satisfying the requirements to the return array.

func checkPairs(in numbers: [Int], forSum target: Int) -> [(Int,Int)] {
    var pairs = [(Int,Int)]()
    for (i, x) in numbers.enumerated() {
        for y in numbers[i+1 ..< numbers.count] {
            if x + y == target {
                pairs.append((x,y))
            }
        }
    }
    return pairs
}

print(checkPairs(in: [1, 2, 4, 4, 7, 5, 3], forSum: 8))

Output:

[(1, 7), (4, 4), (5, 3)]

If you're looking for unique pairs, you can define a custom type holding the pair of numbers and return a Set instead of an Array (the custom type is needed, since you cannot make a Tuple conform to Hashable, which is needed to be able to add elements to a Set).

struct Pair: Hashable {
    let smaller:Int
    let bigger:Int
    
    init(_ a:Int, _ b:Int) {
        if a < b {
            smaller = a
            bigger = b
        } else {
            smaller = b
            bigger = a
        }
    }
}

extension Pair: CustomStringConvertible {
    var description:String {
        return "\((smaller,bigger))"
    }
}

func checkPairs(in numbers: [Int], forSum target: Int) -> Set<Pair> {
    var pairs = Set<Pair>()
    for (i, x) in numbers.enumerated() {
        for y in numbers[i+1 ..< numbers.count] {
            if x + y == target {
                pairs.insert(Pair(x,y))
            }
        }
    }
    return pairs
}

print(checkPairs(in: [1, 2, 4, 4, 7, 5, 3], forSum: 8))
print(checkPairs(in: [1, 2, 4, 4, 7, 5, 3, 4, 1], forSum: 8))

Output:

[(4, 4), (3, 5), (1, 7)]

[(4, 4), (3, 5), (1, 7)]

user_46678350

here is one of options you can do

    let array = [1, 2, 4, 4, 7, 5, 3]
let target = 8


func checkPairs(in numbers: [Int], forSum target: Int) -> String {
    var pairs = ""
    for (i, x) in numbers.enumerated() {
        for y in numbers[i+1 ..< numbers.count] {
            if x + y == target {
                pairs += ("There is a pair that sums \(target): \(x)+\(y)=\(target)\n")
            }
        }
    }
    return pairs
}

print(checkPairs(in: array, forSum: target))

output will be There is a pair that sums 8: 1+7=8 There is a pair that sums 8: 4+4=8 There is a pair that sums 8: 5+3=8

user_66308590
Related