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Day12_SubarraySumsDivisiblebyK.cpp
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Day12_SubarraySumsDivisiblebyK.cpp
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// Given an integer array nums and an integer k, return the number of non-empty subarrays that have a sum divisible by k.
// A subarray is a contiguous part of an array.
// Example 1:
// Input: nums = [4,5,0,-2,-3,1], k = 5
// Output: 7
// Explanation: There are 7 subarrays with a sum divisible by k = 5:
// [4, 5, 0, -2, -3, 1], [5], [5, 0], [5, 0, -2, -3], [0], [0, -2, -3], [-2, -3]
// Example 2:
// Input: nums = [5], k = 9
// Output: 0
// Constraints:
// 1 <= nums.length <= 3 * 104
// -104 <= nums[i] <= 104
// 2 <= k <= 104
// Topics
// Array
// Hash Table
// Prefix Sum
// Solution:
class Solution {
public:
int subarraysDivByK(vector<int>& nums, int k) {
map<int,int> mp;;
mp[0]=1;
int presum=0,count=0,rem;
for(int i=0;i<nums.size();i++){
presum+=nums[i];
rem=presum%k;
if(rem<0){
rem+=k;
}
if(mp.find(rem)!=mp.end()){
count+=mp[rem];
mp[rem]++;
}
else{
mp[rem]=1;
}
}
return count;
}
};