1346. Check If N and Its Double Exist-检查整数及其两倍数是否存在

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

Solution in python:

class Solution:
    def checkIfExist(self, arr: List[int]) -> bool:
        arr.sort()
        print(arr)
        for i in range(len(arr)):
            if arr[i] >= 0:
                for j in range(i+1, len(arr)):
                    if arr[j] >= 0 and arr[i]*2 == arr[j]:
                        print(i, j)
                        return True
            if arr[i] < 0:
                for j in range(i+1, len(arr)):
                    if arr[j] < 0 and arr[i] == arr[j]*2:
                        print(i, j)
                        return True
        return False