#include <bits/stdc++.h>
using namespace std;
 
void isValidPair(int arr[], int k, int n){
	//element , index of last occurence 
	unordered_map<int,int>mpp;
 
	for(int i=0;i<n;i++){
		//if curr el found in map 
		if(mpp.find(arr[i])!=mpp.end()){
			int index=mpp[arr[i]];
			int dist = i-index-1;
			if(dist<=k) cout<<"Valid pair found at index "<<i<<endl;
		}
		else{
			mpp[arr[i]]=i;
		}
	}
}
int main() {
	// your code goes here
	int arr[]={1, 2, 3 ,1,2};
	int k=2;
	isValidPair(arr, k, 5);
	return 0;
}

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