1346. Check If N and Its Double Exist
Description
Given an array arr
of integers, check if there exist 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: For i = 0 and j = 2, arr[i] == 10 == 2 * 5 == 2 * arr[j]
Example 2:
Input: arr = [3,1,7,11] Output: false Explanation: There is no i and j that satisfy the conditions.
Constraints:
2 <= arr.length <= 500
-103 <= arr[i] <= 103
Solutions
Solution 1: Hash Table
We define a hash table $s$ to record the elements that have been visited.
Traverse the array $arr$. For each element $x$, if either double of $x$ or half of $x$ is in the hash table $s$, then return true
. Otherwise, add $x$ to the hash table $s$.
If no element satisfying the condition is found after the traversal, return false
.
The time complexity is $O(n)$, and the space complexity is $O(n)$. Where $n$ is the length of the array $arr$.
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1 2 3 4 5 6 7 8 9 10 |
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1 2 3 4 5 6 7 8 9 10 |
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