add 2409

Author: fishercoder1534

Diff for: paginated_contents/algorithms/3rd_thousand/README.md

@@ -51,6 +51,7 @@
 | 2432 | [The Employee That Worked on the Longest Task](https://leetcode.com/problems/the-employee-that-worked-on-the-longest-task/)                                                                   | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2432.java)                                       || Easy                                 ||
 | 2427 | [Number of Common Factors](https://leetcode.com/problems/number-of-common-factors/)                                                                                                           | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2427.java)                                       || Easy                                 ||
 | 2418 | [Sort the People](https://leetcode.com/problems/sort-the-people/)                                                                                                       | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2418.java)                                       || Easy                                 ||
+| 2409 | [Count Days Spent Together](https://leetcode.com/problems/count-days-spent-together/)                                                                                                       | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2409.java)                                       || Easy                                 ||
 | 2404 | [Most Frequent Even Element](https://leetcode.com/problems/most-frequent-even-element/)                                                                                                       | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2404.java)                                       || Easy                                 ||
 | 2399 | [Check Distances Between Same Letters](https://leetcode.com/problems/check-distances-between-same-letters/)                                                                                   | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2399.java)                                       || Medium                               ||
 | 2395 | [Find Subarrays With Equal Sum](https://leetcode.com/problems/find-subarrays-with-equal-sum/)                                                                                                 | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/thirdthousand/_2395.java)                                       || Easy                                 ||

Diff for: src/main/java/com/fishercoder/solutions/thirdthousand/_2409.java

@@ -0,0 +1,58 @@
+package com.fishercoder.solutions.thirdthousand;
+
+public class _2409 {
+    public static class Solution1 {
+        /**
+         * Brute force: check each day of the 365 days if both of them are in Rome.
+         */
+        public int countDaysTogether(String arriveAlice, String leaveAlice, String arriveBob, String leaveBob) {
+            int[] monthToDays = new int[]{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
+            int days = 0;
+            String[] arriveAliceParts = arriveAlice.split("-");
+            String[] leaveAliceParts = leaveAlice.split("-");
+            String[] arriveBobParts = arriveBob.split("-");
+            String[] leaveBobParts = leaveBob.split("-");
+            for (int i = 1; i < monthToDays.length; i++) {
+                int daysInMonth = monthToDays[i];
+                for (int j = 1; j <= daysInMonth; j++) {
+                    if (bothInRome(i, j, arriveAliceParts, leaveAliceParts, arriveBobParts, leaveBobParts)) {
+                        days++;
+                    }
+                }
+            }
+            return days;
+        }
+
+        private boolean bothInRome(int month, int day, String[] arriveAliceParts, String[] leaveAliceParts, String[] arriveBobParts, String[] leaveBobParts) {
+            int aliceArriveMonth = Integer.parseInt(arriveAliceParts[0]);
+            int aliceArriveDay = Integer.parseInt(arriveAliceParts[1]);
+            int aliceLeaveMonth = Integer.parseInt(leaveAliceParts[0]);
+            int aliceLeaveDay = Integer.parseInt(leaveAliceParts[1]);
+
+            int bobArriveMonth = Integer.parseInt(arriveBobParts[0]);
+            int bobArriveDay = Integer.parseInt(arriveBobParts[1]);
+            int bobLeaveMonth = Integer.parseInt(leaveBobParts[0]);
+            int bobLeaveDay = Integer.parseInt(leaveBobParts[1]);
+
+            return inRome(aliceArriveMonth, aliceArriveDay, aliceLeaveMonth, aliceLeaveDay, month, day) && inRome(bobArriveMonth, bobArriveDay, bobLeaveMonth, bobLeaveDay, month, day);
+        }
+
+        private boolean inRome(int arriveMonth, int arriveDay, int leaveMonth, int leaveDay, int month, int day) {
+            if (month < arriveMonth || month > leaveMonth) {
+                return false;
+            }
+            if (month > arriveMonth && month < leaveMonth) {
+                return true;
+            }
+            if (month == arriveMonth) {
+                if (arriveMonth == leaveMonth) {
+                    return arriveDay <= day && leaveDay >= day;
+                } else {
+                    return arriveDay <= day;
+                }
+            }
+            //now, only this case: month == leaveMonth
+            return day <= leaveDay;
+        }
+    }
+}

Diff for: src/test/java/com/fishercoder/thirdthousand/_2409Test.java

@@ -0,0 +1,42 @@
+package com.fishercoder.thirdthousand;
+
+import com.fishercoder.solutions.thirdthousand._2409;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class _2409Test {
+    private static _2409.Solution1 solution1;
+
+    @BeforeEach
+    public void setup() {
+        solution1 = new _2409.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(3, solution1.countDaysTogether("08-15", "08-18", "08-16", "08-19"));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals(0, solution1.countDaysTogether("10-01", "10-31", "11-01", "12-31"));
+    }
+
+    @Test
+    public void test3() {
+        assertEquals(49, solution1.countDaysTogether("09-01", "10-19", "06-19", "10-20"));
+    }
+
+    @Test
+    public void test4() {
+        assertEquals(27, solution1.countDaysTogether("08-06", "12-08", "08-06", "09-01"));
+    }
+
+    @Test
+    public void test5() {
+        assertEquals(27, solution1.countDaysTogether("08-06", "12-08", "02-04", "09-01"));
+    }
+
+}