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Bitwise ORs of Subarrays in C++
Suppose we have an array A of non-negative integers. For every (contiguous) subarray say B = [A[i], A[i+1], ..., A[j]] (with i <= j), we will do the bitwise OR of all the elements in B, obtaining a result A[i] | A[i+1] | ... | A[j]. We have to find the number of possible results. (Results that occur more than once are only counted once in the final answer.)
So if the input is like [1,1,2], then the result will be 3 as subarrays are [1], [1], [2], [1,1], [1,2], [1,1,2], then the results will be 1,1,2,1,3,3, then there are three distinct results.
To solve this, we will follow these steps −
Create two sets ret and curr2
for i in range 0 to size of array
make a set curr1, insert A[i] into it
for each element e in curr2 −
insert (e OR A[i]) into curr1
for each element e curr1
insert e in ret
curr2 := curr1
return size of ret
Example
Let us see the following implementation to get better understanding −
#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
int subarrayBitwiseORs(vector<int>& A) {
unordered_set <int> ret;
unordered_set <int> curr2;
for(int i = 0; i < A.size(); i++){
unordered_set <int> curr1;
curr1.insert(A[i]);
unordered_set<int>::iterator it = curr2.begin();
while(it != curr2.end()){
curr1.insert(*it | A[i]);
it++;
}
it = curr1.begin();
while(it != curr1.end()){
ret.insert(*it);
it++;
}
curr2 = curr1;
}
return ret.size();
}
};
main(){
vector<int> v = {1,1,2};
Solution ob;
cout << (ob.subarrayBitwiseORs(v));
}Input
[1,1,2]
Output
3
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