1248. Count Number of Nice Subarrays | LeetCode Solution

Given an array of integers nums and an integer k. A continuous subarray is called nice if there are k odd numbers on it.

Return the number of nice sub-arrays.

 

Example 1:

Input: nums = [1,1,2,1,1], k = 3
Output: 2
Explanation: The only sub-arrays with 3 odd numbers are [1,1,2,1] and [1,2,1,1].

Example 2:

Input: nums = [2,4,6], k = 1
Output: 0
Explanation: There is no odd numbers in the array.

Example 3:

Input: nums = [2,2,2,1,2,2,1,2,2,2], k = 2
Output: 16

 

Constraints:

  • 1 <= nums.length <= 50000
  • 1 <= nums[i] <= 10^5
  • 1 <= k <= nums.length

class Solution {
public:
    int numberOfSubarrays(vector<int>& nums, int k) {
        for(int i=0; i<nums.size(); i++){
            if(nums[i]%2==0)nums[i]=0;
            else nums[i]=1;
        }
        
         unordered_map<int,int>mymap;
        
        int sum=0,ans=0;
        mymap[sum]=1;
        for(int i=0; i<nums.size(); i++){
            sum+=nums[i];
            auto it=mymap.find(sum-k);
            if(it!=mymap.end())ans+=mymap[sum-k];
            mymap[sum]++;
        }
        return ans;
    }
};