Table of Contents
中文版：
给你一个整数数组 arr，请你检查是否存在两个整数 N 和 M，满足 N 是 M 的两倍（即，N = 2 * M）。
更正式地，检查是否存在两个下标 i 和 j 满足：
i != j
0 <= i, j < arr.length
arr[i] == 2 * arr[j]
示例 1：
输入：arr = [10,2,5,3]
输出：true
解释：N = 10 是 M = 5 的两倍，即 10 = 2 * 5 。
示例 2：
输入：arr = [7,1,14,11]
输出：true
解释：N = 14 是 M = 7 的两倍，即 14 = 2 * 7 。
示例 3：
输入：arr = [3,1,7,11]
输出：false
解释：在该情况下不存在 N 和 M 满足 N = 2 * M 。
提示：
2 <= arr.length <= 500
-10^3 <= arr[i] <= 10^3
英文版：
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
My answer：
class Solution:
def checkIfExist(self, arr: List[int]) -> bool:
l = len(arr)
for i in range(l):
for j in range(l):
if (arr[j] == 2*arr[i]) and (i != j):
return True
return False
解题报告：
本题直接模拟题目描述即可。
需注意的是要 i != j，否则 [0,1]会得到 true，因为 0 是 0 的 2 倍。
