C++ CODE :

// CPP program to find longest subarray with
// k or less distinct elements.
#include <bits/stdc++.h>
using namespace std;
// function to print the longest sub-array
void longest(int a[], int n, int k)
{
unordered_map<int, int> freq;
int start = 0, end = 0, now = 0, l = 0;
for (int i = 0; i < n; i++) {
// mark the element visited
freq[a[i]]++;
// if its visited first time, then increase
// the counter of distinct elements by 1
if (freq[a[i]] == 1)
now++;
// When the counter of distinct elements
// increases from k, then reduce it to k
while (now > k) {
// from the left, reduce the number of
// time of visit
freq[a[l]]--;
// if the reduced visited time element
// is not present in further segment
// then decrease the count of distinct
// elements
if (freq[a[l]] == 0)
now--;
// increase the subsegment mark
l++;
}
// check length of longest sub-segment
// when greater than previous best
// then change it
if (i - l + 1 >= end - start + 1)
end = i, start = l;
}
// print the longest sub-segment
cout<<(end-start+1);
}
// driver program to test the above function
int main()
{
int n,k;
cin>>n>>k ;
k = k - 1 ;
int a[n];
//= { 6, 5, 1, 2, 3, 2, 1, 4, 5 };
int i = 0 ;
while(i<=n-1){
cin>>a[i];
i++;
}
longest(a, n, k);
return 0;
}