878748. Day before N days
Day before N days
Summary
Given a number N, find the day that is one day before N. This problem involves basic arithmetic operations and requires no advanced data structures or algorithms.
Detailed Explanation
The problem seems straightforward, but it's essential to understand what "one day before N" means. It implies that if today is the Nth day of a month, we need to find out what was the (N-1)th day of the previous month. For example, if today is the 31st day of January (which has 31 days), then one day before would be the 30th day of December (which also has 31 days).
To solve this problem, we can simply subtract 1 from N. This approach assumes that we know the number of days in each month. If we don't know, we can use a simple array or dictionary to store the number of days in each month and then adjust our calculation accordingly.
Here's the step-by-step breakdown:
- Subtract 1 from
Nto get(N-1). - Check if
(N-1)is less than 28 (assuming a non-leap year). If it is, add 31 to get the correct day of the previous month. - Otherwise, check if
(N-1)is between 28 and 59 (inclusive). If it is, add 30 to get the correct day of the previous month. - If
(N-1)is greater than 59, add 28 to get the correct day of the previous month.
The time complexity of this solution is O(1) because we're performing a constant number of operations regardless of the input size. The space complexity is also O(1) as we're not using any extra space that scales with the input size.
Optimized Solutions
Java
public class DayBeforeN {
public static String dayBefore(int n) {
int daysInMonth = 0;
if (n <= 7) {
daysInMonth = 31;
} else if (n <= 18) {
daysInMonth = 30;
} else {
daysInMonth = 28;
}
return String.valueOf(n - 1);
}
}