Create DIV_PAIR_SUM.cpp

Math/DIV_PAIR_SUM.cpp

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+#include <bits/stdc++.h>
+
+using namespace std;
+
+vector<string> split_string(string);
+
+
+
+int main()
+{
+    string nk_temp;
+    getline(cin, nk_temp);
+
+    vector<string> nk = split_string(nk_temp);
+
+    int n = stoi(nk[0]);
+
+    int k = stoi(nk[1]);
+
+    string a_temp_temp;
+    getline(cin, a_temp_temp);
+
+    vector<string> a_temp = split_string(a_temp_temp);
+
+    vector<int> a(n);
+
+    int arr[k]={0}; //index is remainder from integer%k and value is count of number of ints
+
+
+    for (int i = 0; i < n; i++) 
+    {
+        int a_item = stoi(a_temp[i]);
+
+        a[i] = a_item;
+        int rem = a_item % k;
+        arr[rem]=arr[rem]+1;
+    }
+
+    int count= arr[0]*(arr[0]-1)/2;
+    //cout<<count<<endl;
+    for(int i=1;i<(k+1)/2;i++)
+    {
+        count+=arr[i]*arr[k-i];
+    }
+    //cout<<count<<endl;
+    if(k%2==0)
+    {
+        count+=(arr[k/2]*(arr[k/2]-1))/2;
+    }
+
+    cout<<count;
+
+    return 0;
+
+}