# Number of K-Divisible Pairs - Amazon Top Interview Questions

### Problem Statement :

```You are given a list of integers nums and an integer k. Return the number of pairs i < j such that (nums[i] + nums[j]) % k = 0

Constraints

n ≤ 100,000 where n is the length of nums

1 ≤ k ≤ 100

Example 1

Input

nums = [2, 4, 5, 1, 2]

k = 6

Output

3

Explanation

We have the following pairs

[2, 4]
[4, 2]
[5, 1]

Example 2

Input

nums = [3, 7, 2]

k = 7

Output

0```

### Solution :

```                        ```Solution in C++ :

int solve(vector<int>& nums, int k) {
unordered_map<int, int> m;
int ans = 0;
for (auto& n : nums) {
ans += m[(k - n % k) % k];
m[n % k] += 1;
}
return ans;
}```
```

```                        ```Solution in Java :

import java.util.*;

class Solution {
public int solve(int[] nums, int k) {
int res = 0;
Map<Integer, Integer> map = new HashMap<>();
for (int i = 0; i < nums.length; i++) {
int mod = nums[i] % k;
if (map.containsKey((k - mod) % k)) {
res += map.get((k - mod) % k);
}
map.put(mod, map.getOrDefault(mod, 0) + 1);
}
return res;
}
}```
```

```                        ```Solution in Python :

class Solution:
def solve(self, nums, k):
c = 0
a = {}
for x in nums:
y = x % k
c += a.get((k - y) % k, 0)
a[y] = a.get(y, 0) + 1
return c```
```

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