LC_Check_If_N_Exists_and_Double.go

"""
1346. Check If N and Its Double Exist

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]
 

Example 1:

Input: arr = [10,2,5,3]
Output: true
Explanation: N = 10 is the double of M = 5,that is, 10 = 2 * 5.
Example 2:

Input: arr = [7,1,14,11]
Output: true
Explanation: N = 14 is the double of M = 7,that is, 14 = 2 * 7.
Example 3:

Input: arr = [3,1,7,11]
Output: false
Explanation: In this case does not exist N and M, such that N = 2 * M.
 

Constraints:

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


func checkIfExist(arr []int) bool {
    set := map[int]bool{}
    for _,num := range arr {
        if num == 0 {
            if _,ok := set[0]; ok {
                return true
            }
            set[num] = true
            continue
        }
        set[num] = true
        if _,ok := set[num * 2]; ok {
           return true 
        }
        
        if (num % 2 == 0) {
            if _,ok := set[num / 2]; ok {
                return true
            }
        }
    }
    return false
}