subarray_questions.cpp

class Solution {
public:
    int subarraysDivByK(vector<int>& nums, int k)
    {
        unordered_map<int,int> m; m[0]++;
        int sum=0,count=0;
        for(int i=0;i<nums.size();i++)
        {
            //ith index->as end
            sum+=nums[i];
            sum=sum%k;
            if(sum<0) sum+=k;
            if(m.find(sum%k)!=m.end())
            {
                count+=m[sum%k];
                m[sum%k]++;
            }
            else
            {
                m[sum%k]++;
            }
        }
        return count;
    }
};