LeetCode Ts-3688. Bitwise OR of Even Numbers in an Array

    AllenLi
    CodingLeetCode Js-Math

    You are given an integer array nums.
    Return the bitwise OR of all even numbers in the array.
    If there are no even numbers in nums, return 0.

    你給予一個整數的陣列叫做 nums。
回傳所有偶數的位元 OR 值，
若沒有偶數則回傳 0。

    Example 1:

    Input: nums = [1,2,3,4,5,6]
Output: 6
Explanation:
The even numbers are 2, 4, and 6. Their bitwise OR equals 6.

    Example 2:

    Input: nums = [7,9,11]
Output: 0
Explanation:
There are no even numbers, so the result is 0.

    Example 3:

    Input: nums = [1,8,16]
Output: 24
Explanation:
The even numbers are 8 and 16. Their bitwise OR equals 24.

    solution:
    根據題目要求，我們需要先篩選出陣列 nums 中的偶數，
    然後將這些偶數透過位元運算計算它們的 OR 值。若陣列中沒有偶數，則結果為 0。

    Code 1: BigO(n)

    function evenNumberBitwiseORs(nums: number[]): number {
    let result: number = 0;
    for (const num of nums) {
        if (num % 2 === 0) {
            result = result | num;
        }
    }
    return result;
};

    Code 2: BigO(n)

    function evenNumberBitwiseORs(nums: number[]): number {
    return nums.reduce((a, c) => c & 1 ? a : a | c, 0);
};

    FlowChart:
    Example 1

    Input: nums = [1,2,3,4,5,6]

1 % 2 !== 0 pass
2 % 2 === 0 result = 0 | 2 = 2
   0  0000
OR 2  0010
----------
      0010 -> 2

3 % 2 !== 0 pass
4 % 2 === 0 result = 2 | 4 = 6
   2  0010
OR 4  0100
----------
      0110 -> 6

5 % 2 !== 0 pass
6 % 2 === 0 result = 6 | 6 = 6
   6  0110
OR 6  0110
----------
      0110 -> 6

return 6;

    Example 2

    Input: nums = [7,9,11]

7  % 2 !== 0 pass
9  % 2 !== 0 pass
11 % 2 !== 0 pass

return 0;

    Example 3

    Input: nums = [1,8,16]

1 % 2 !== 0 pass
2 % 2 === 0 result = 0 | 8 = 8
   0  0000
OR 8  1000
----------
      1000 -> 8

16 % 2 === 0 result = 8 | 16 = 24
    8 01000
OR 16 10000
----------
      11000 -> 24

return 24;

    Remark: 二進位表示

      
二進位只有 0 和 1 的表示，每一位從右到左分別代表 2^0, 2^1, 2^2, 2^3…。  
將有 1 的位元加總即可得到十進位值。
value 8   4   2   1
2^n   2^3 2^2 2^1 2^0

      0   0   0   1
-------------------
                  1 -> 1

      0   0   1   1  
-------------------
              2 + 1 -> 3

    Related Posts