Today I have done leetcode's November LeetCoding Challenge with cpp.

November LeetCoding Challenge 10

Description

Shortest Subarray With OR at Least K II

You are given an array nums of non-negative integers and an integer k.

An array is called special if the bitwise OR of all of its elements is at least k.

Return the length of the shortest special non-empty subarray of nums, or return -1 if no special subarray exists.

Example 1:

Example 2:

Example 3:

Constraints:

• 1 <= nums.length <= 2 * 105
• 0 <= nums[i] <= 109
• 0 <= k <= 109

Solution

class Solution {
  int k;
  bitset<30> B;
  void update(vector<int> &freq, unsigned x, bool add = true) {
    bitset<30> b(x);
    for(int i = 0; i < 30; ++i) {
      freq[i] += add ? b[i] : -b[i];
    }
  }

  bool check(vector<int> &freq) {
    int b = 0;
    for(int i = 0; i < 30; ++i) {
      if(freq[i] > 0) b |= (1 << i);
    }
    return b >= k;
  }
public:
  int minimumSubarrayLength(vector<int>& nums, int k) {
    if(!k) return 1;
    this->k = k;
    B = bitset<30>(k);

    vector<int> freq(30);
    int len = nums.size();
    int answer = INT_MAX;
    for(int begin = 0, end = 0; end < len; ++end) {
      int x = nums[end];
      if(x >= k) return 1;
      update(freq, x);
      while(begin < end && check(freq)) {
        answer = min(answer, end - begin + 1);
        update(freq, nums[begin], false);
        begin += 1;
      }
    }
    return answer == INT_MAX ? -1 : answer;
  }
};