Arrays101 Check If N and Its Double Exist in go

inAccepted Solutions Runtime Distribution

Accepted Solutions Memory Distribution

Given an array arr of integers, check if there exists two integers N and M such that N is the double of M ( i.e. N = 2 * M).

More formally check if there exists two indices i and j such that :

i != j
0 <= i, j < arr.length
arr[i] == 2 * arr[j]

Constraints:
2 <= arr.length <= 500
-10^3 <= arr[i] <= 10^3

Code

func checkIfExist(arr []int) bool {

    e := len(arr)

    for l := 0; l < e; l++ {
        for r := e - 1; r > l; r-- {
            switch {
            case arr[l] == 0 && arr[r] == 0:
                return true
            case arr[l] == 0 && arr[r] != 0 || arr[r] == 0 && arr[l] != 0:
                break
            case arr[l]%arr[r] == 0 || arr[r]%arr[l] == 0:
                if arr[l]/arr[r] == 2 || arr[r]/arr[l] == 2 {
                    return true
                }
            }
        }
    }
    return false
}

• First I wanted to used switch for simplicity.
• So I made switch condition as l>r and l/r.
• But test cases has negative numbers.
• I changed all to check normal conditions for both positive and negative numbers.
• l is left as start of array and r is right as end of array.

Sample 0 ms submission

func checkIfExist(arr []int) bool {
  container := make(map[int]int, len(arr))
    for i := 0; i < len(arr); i++ {
        if _, ok := container[arr[i]*2]; ok  {
            return true
    }else if _, ok := container[arr[i]/2]; ok && arr[i]%2 == 0 {
            return true
    } else {
            container[arr[i]] = i
        }
    }
    return false
}

• I think this code is really clean
• First, If condition checks that there is arr[i]*2 value as a key of map.
• If not, Second, arr[i] will be devided by 2 also check remainder is zero because devide returns only quotient.
• Lastly, If there is no key, arr[i] value will be added in map with index(actually no meaning).

Sample 1 ms submission & Sample 2900 KB submission

func checkIfExist(arr []int) bool {
    for i := 0; i < len(arr); i++ {
        for j := i + 1; j < len(arr); j++ {
            if arr[i] == arr[j] * 2 || arr[j] == arr[i] * 2 {
                return true
            }
        }
    }
    return false
}

• This code also is very simple.
• Just check if arr values are doubled compared to other values.

Go routine exercise

func checkIfExist(arr []int) bool {

    ch := make(chan bool)
    go checker(arr, ch)

    return <-ch

}

func checker(arr []int, ch chan bool) {
    e := len(arr)
    for l := 0; l < e; l++ {
        for r := e - 1; r > l; r-- {
            switch {
            case arr[l] == 0 && arr[r] == 0:
                ch <- true
            case arr[l] == 0 && arr[r] != 0 || arr[r] == 0 && arr[l] != 0:
                break
            case arr[l]%arr[r] == 0 || arr[r]%arr[l] == 0:
                if arr[l]/arr[r] == 2 || arr[r]/arr[l] == 2 {
                    ch <- true
                }
            }
        }
    }
    ch <- false

}

https://go.dev/play/p/NzR5mkdBz3M

Modification code

func checkIfExist(arr []int) bool {
    e := len(arr)
    for l := 0; l < e; l++ {
        for r := e - 1; r > l; r-- {
            switch {
            case arr[l]*2 == arr[r] || arr[r]*2 == arr[l]:
                return true
            }
        }
    }
    return false
}