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Subarray Sums Divisible by K in C++
Suppose we have an array A of integers. We have to find the number of contiguous non-empty subarray, that have a sum divisible by k. If A = [4,5,0,-2,-3,1] and k = 5, then the output will be 7. There are seven subarrays. [[4,5,0,-2,-3,1], [5], [5,0],[5,0,-2,-3], [0], [0,-2,-3], [-2,-3]]
To solve this, we will follow these steps −
- make one map m and set m[0] as 1
- temp := 0, ans := 0, and n := size of array a
- for i in range 0 to n – 1
- temp := temp + a[i]
- x := (temp mod k + k) mod k
- ans := ans + m[x]
- increase m[x] by 1
- return ans
Let us see the following implementation to get better understanding −
Example
#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
int subarraysDivByK(vector<int>& a, int k) {
unordered_map <int, int> m;
m[0] = 1;
int temp = 0;
int ans = 0;
int n = a.size();
for(int i = 0; i < n; i++){
temp += a[i];
int x = (temp % k + k) % k;
ans += m[x];
m[x]++;
}
return ans;
}
};
main(){
vector<int> v = {4,5,0,-2,-3,1};
Solution ob;
cout <<(ob.subarraysDivByK(v, 5));
}Input
[4,5,0,-2,-3,1] 5
Output
7
Updated on: 30-Apr-2020
416 Views
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