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Problem Brief

Get Discount Pairs 🍊

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Amazon is offering a discount on every purchase of a pair of products whose price sum is divisible by x. Given the price of n products in the store, find the number of pairs (i, j) where i < j and prices[i] + prices[j] is divisible by x.

Function Description

Complete the function getDiscountPairs in the editor.

getDiscountPairs has the following parameter(s):

  1. 1. int x: sum of a pair of integers should be divisible by this number
  2. 2. int prices[n]: the prices of the products

Returns

int: the number of pairs in the array whose sum is divisible by x

1Example 1

Input
x = 60, prices = [31, 25, 85, 29, 35]
Output
3
Explanation
Example 1 illustration
The answer is 3 based on the pairs (31, 29), (25, 35), and (85, 35). Each pair sums to a number divisible by x.

Constraints

Limits and guarantees your solution can rely on.

1 ≤ x ≤ 2 * 109

1 ≤ n ≤ 105

1 ≤ prices[i] ≤ 9 

public int getDiscountPairs(int x, int[] prices) {
    // write your code here
}
Input

x

60

prices

[31, 25, 85, 29, 35]

Output

3

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