<p>Given an integer array <code>nums</code> and an integer <code>k</code>, return <em>the number of <strong>good subarrays</strong> of </em><code>nums</code>.</p>

<p>A <strong>good array</strong> is an array where the number of different integers in that array is exactly <code>k</code>.</p>

<ul>
	<li>For example, <code>[1,2,3,1,2]</code> has <code>3</code> different integers: <code>1</code>, <code>2</code>, and <code>3</code>.</li>
</ul>

<p>A <strong>subarray</strong> is a <strong>contiguous</strong> part of an array.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,2,1,2,3], k = 2
<strong>Output:</strong> 7
<strong>Explanation:</strong> Subarrays formed with exactly 2 different integers: [1,2], [2,1], [1,2], [2,3], [1,2,1], [2,1,2], [1,2,1,2]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,2,1,3,4], k = 3
<strong>Output:</strong> 3
<strong>Explanation:</strong> Subarrays formed with exactly 3 different integers: [1,2,1,3], [2,1,3], [1,3,4].
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 2 * 10<sup>4</sup></code></li>
	<li><code>1 &lt;= nums[i], k &lt;= nums.length</code></li>
</ul>

class Solution {
public:
    int subarraysWithKDistinct(vector<int>& a, int k) {
        int n=a.size(),i=0,j=0,ans=0;
        vector<int> mp(n+1,0);
        unordered_set<int> st;
        while(i<n){
            if(st.size()<k){
                st.insert(a[i]);
                mp[a[i]]++;
                i++;
            }
            else{
                int ct2=1;
                while(mp[a[j]]>1){
                    ct2++;
                    mp[a[j]]--;
                    j++;
                }
                ans+=ct2;
                while(i<n && mp[a[i]]){
                    mp[a[i]]++;
                    i++;
                    while(mp[a[j]]>1){
                        ct2++;
                        mp[a[j]]--;
                        j++;
                    }
                    ans+=ct2;
                }
                st.erase(a[j]);
                mp[a[j]]--;
                j++;
            }
            
        }
        if(st.size()==k){
            int ct2=1;
            while(j<n && mp[a[j]]>1){
                mp[a[j]]--;
                j++;
                ct2++;
            }
            ans+=ct2;
        }
        return ans;
    }
};
48775