<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 {
    private:
      int subarray(vector<int> arr, int k){
             int n = arr.size();
             map<int, int> mp;
             int tail = 0 , head = -1 , ans = 0;
             int distCnt = 0;
             while(tail<n){
                while(head+1<n && (distCnt<k || mp[arr[head+1]]!=0)){
                    head++;
                    if(mp[arr[head]]==0) distCnt++;
                    mp[arr[head]]++;
                }
                ans = ans +(head-tail+1);
                if(tail>head){
                    tail++;
                }else{
                    mp[arr[tail]]--;
                    if(mp[arr[tail]]==0) distCnt--;
                    tail++;
                }
             }
             return ans;
      }
public:
    int subarraysWithKDistinct(vector<int>& nums, int k) {
        if(k==1){
            return subarray(nums,k);
        }
         return subarray(nums,k)-subarray(nums, k-1);
    }
};
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