找出月份中的整数差

Question

I have two vectors that represent months ie 1 as January 2 as February, etc... how do we find the difference between months without getting negative values?

Example

dates1 = [1, 3, 1];

dates2 = [12, 1, 0];

Expected: dates2 - dates1 = [11, 10, 11]

Actual: [11, -2, -1]

Answer 1

If you have two months a and b , and b is after a , and b may possibly be in the following year, you can just use something like:

diff = (b + 12 - a) % 12;

The adding of twelve to b ensures that it is greater than a (effectively moving it into the following year) and the use of modulo ensures the adding of twelve doesn't move it two years beyond a .

Answer 2

You can use modulo arithmetic:

const int MONTHS_PER_YEAR = 12;
int difference = ((month_1 + MONTHS_PER_YEAR) - month_2) % MONTHS_PER_YEAR;