Count Pair With given Sum using map

#include<bits/stdc++.h> using namespace std; void fun(int arr[],int n,int k) { } int main() { int arr[]={1,2,5,4,0}; int n=5; int k=5; unordered_map<int,int>m; int c=0; for(int i=0;i<n;i++) { c+=m[k-arr[i]]; m[arr[i]]++; } cout<<c; return 0; }