LeetCode-in-Java

2568. Minimum Impossible OR

Medium

You are given a 0-indexed integer array nums.

We say that an integer x is expressible from nums if there exist some integers 0 <= index1 < index2 < ... < indexk < nums.length for which nums[index1] | nums[index2] | ... | nums[indexk] = x. In other words, an integer is expressible if it can be written as the bitwise OR of some subsequence of nums.

Return the minimum positive non-zero integer that is not expressible from nums.

Example 1:

Input: nums = [2,1]

Output: 4

Explanation: 1 and 2 are already present in the array. We know that 3 is expressible, since nums[0] | nums[1] = 2 | 1 = 3. Since 4 is not expressible, we return 4.

Example 2:

Input: nums = [5,3,2]

Output: 1

Explanation: We can show that 1 is the smallest number that is not expressible.

Constraints:

• 1 <= nums.length <= 105
• 1 <= nums[i] <= 109

Solution

import java.util.HashSet;
import java.util.Set;

public class Solution {
    public int minImpossibleOR(int[] nums) {
        Set<Integer> set = new HashSet<>();
        for (int n : nums) {
            if (n == 1 || (n & 1) == 0) {
                set.add(n);
            }
        }
        int powerOfTwo = 1;
        while (true) {
            if (!set.contains(powerOfTwo)) {
                return powerOfTwo;
            }
            powerOfTwo *= 2;
        }
    }
}

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