LeetCode Entry

2409. Count Days Spent Together

24.10.2026 easy 2026 kotlin rust

Days range intersection

2409. Count Days Spent Together easy substack youtube

https://dmitrysamoylenko.com/leetcode/

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Problem TLDR

Days range intersection

Intuition

Convert to day of a year

Approach

• we can compare strings directly

Complexity

• Time complexity: \(O(1)\)

• Space complexity: \(O(1)\)

Code

    fun countDaysTogether(aa: String, la: String, ab: String, lb: String): Int {
        val days = listOf(0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31)
        fun d(s: String) = days.take(s.take(2).toInt()).sum() + s.drop(3).toInt()
        return max(0, d(minOf(la, lb)) - d(maxOf(aa, ab)) + 1)
    }

    pub fn count_days_together(aa: String, la: String, ab: String, lb: String) -> i32 {
        let d = |s: &str| [0,31,59,90,120,151,181,212,243,273,304,334][s[..2].parse::<usize>().unwrap() - 1] + s[3..].parse::<i32>().unwrap();
        (d(&la.min(lb)) - d(&aa.max(ab)) + 1).max(0)
    }