1346. Check If N and Its Double Exist

Problem

Tags: Array, Hash Table, Two Pointers, Binary Search, Sorting

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

Code

C

// 1346. Check If N and Its Double Exist (7/7/54000)
// Runtime: 11 ms (23.47%) Memory: 6.38 MB (18.05%) 

bool checkIfExist(int arr[], int arrSize){
    bool table[4002] = { 0 };
    
    for (size_t i = 0; i < arrSize; i++) {
        if (table[arr[i] + 2000]) {
            return true;
        }
        
        if (arr[i] % 2 == 0) {
            table[(arr[i] / 2) + 2000] = true;
        }
        table[(arr[i] * 2) + 2000] = true;
    }
    
    return false;
}