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find-a-value-of-a-mysterious-function-closest-to-target.cpp
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find-a-value-of-a-mysterious-function-closest-to-target.cpp
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// Time: O(nlogm), m is the max value of arr
// Space: O(logm)
class Solution {
public:
int closestToTarget(std::vector<int>& arr, int target) {
static const int LOGM = 20;
BitCount count(LOGM);
int result = numeric_limits<int>::max();
for (int left = 0, right = 0; right < arr.size(); ++right) {
count += arr[right];
while (left <= right) {
const auto& f = count.bitAnd();
result = min(result, abs(f - target));
if (f >= target) {
break;
}
count -= arr[left++];
}
}
return result;
}
private:
class BitCount {
public:
BitCount(int n)
: l_(0)
, n_(n)
, count_(n) {
}
int bitAnd() const {
int num = 0;
for (int i = 0; i < n_; ++i) {
if (count_[i] == l_) {
num |= 1 << i;
}
}
return num;
}
void operator+=(int num) {
++l_;
for (int i = 0; i < n_; ++i) {
if (num & (1 << i)) {
++count_[i];
}
}
}
void operator-=(int num) {
--l_;
for (int i = 0; i < n_; ++i) {
if (num & (1 << i)) {
--count_[i];
}
}
}
private:
int l_;
int n_;
vector<int> count_;
};
};
// Time: O(nlogm), m is the max value of arr
// Space: O(logm)
class Solution2 {
public:
int closestToTarget(vector<int>& arr, int target) {
int result = numeric_limits<int>::max();
unordered_set<int> dp; // at most O(logm) dp states
for (const auto& x : arr) {
unordered_set<int> new_dp = {x};
for (const auto& f: dp) {
new_dp.emplace(f & x);
}
for (const auto& f : new_dp) {
result = min(result, abs(f - target));
}
dp = move(new_dp);
}
return result;
}
};