1318. Minimum Flips to Make a OR b Equal to c

LeetCode 1318. Minimum Flips to Make a OR b Equal to c

Description

Given 3 positives numbers a, b and c. Return the minimum flips required in some bits of a and b to make ( a OR b == c ). (bitwise OR operation). Flip operation consists of change any single bit 1 to 0 or change the bit 0 to 1 in their binary representation.

Example 1:

Input: a = 2, b = 6, c = 5
Output: 3
Explanation: After flips a = 1 , b = 4 , c = 5 such that (a OR b == c)

Example 2:

Input: a = 4, b = 2, c = 7
Output: 1

Example 3:

Input: a = 1, b = 2, c = 3
Output: 0

Constraints:

• 1 <= a <= 10^9

• 1 <= b <= 10^9

• 1 <= c <= 10^9

Tags

Bit Manipulation

Solution

Check the bits one by one (via (x>>i)&1), and:

• if c[i] == 1 and a[i] == b[i] == 0, then increase the counter by 1;

• if c[i] == 0 and any of a[i] == 1 or b[i] == 1 will let the counter to increment itself by 1.

Complexity

• Time complexity: $O(1)$, no greater than 32 times;

• Space complexity: $O(1)$

Code

func minFlips(a int, b int, c int) int {
	var ans int
	for i := 0; i < 31; i++ {
		if (c>>i)&1 == 1 && (a>>i)&1 == 0 && (b>>i)&1 == 0 {
			ans++
		} else if (c>>i)&1 == 0 {
			if (a>>i)&1 == 1 {
				ans++
			}
			if (b>>i)&1 == 1 {
				ans++
			}
		}
	}
	return ans
}