一、题目
Given an integer array nums and an integer k, return the number of good subarrays of nums.
A good array is an array where the number of different integers in that array is exactly k.
For example, [1,2,3,1,2] has 3 different integers: 1, 2, and 3.
A subarray is a contiguous part of an array.
Example 1:
Input: nums = [1,2,1,2,3], k = 2
Output: 7
Explanation: 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]
Example 2:
Input: nums = [1,2,1,3,4], k = 3
Output: 3
Explanation: Subarrays formed with exactly 3 different integers: [1,2,1,3], [2,1,3], [1,3,4].
Constraints:
1 <= nums.length <= 2 * 104
1 <= nums[i], k <= nums.length文章来源：https://www.toymoban.com/news/detail-807959.html
二、题解
恰好有k个不同元素的子数组的个数 = 最多有k个不同元素的子数组的个数 - 最多有k-1个不同元素的子数组的个数文章来源地址https://www.toymoban.com/news/detail-807959.html
class Solution {
public:
int subarraysWithKDistinct(vector<int>& nums, int k) {
return subarraysWithMostKDistinct(nums,k) - subarraysWithMostKDistinct(nums,k-1);
}
int subarraysWithMostKDistinct(vector<int>& nums,int k){
unordered_map<int,int> map;
int res = 0,collect = 0;
for(int l = 0,r = 0;r < nums.size();r++){
if(++map[nums[r]] == 1) collect++;
while(collect > k){
if(--map[nums[l++]] == 0) collect--;
}
res += r - l + 1;
}
return res;
}
};
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