2409_Count_Days_Spent_Together

python/2409_Count_Days_Spent_Together.py

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+class Solution:
+    def countDaysTogether(self, arriveAlice: str, leaveAlice: str, arriveBob: str, leaveBob: str) -> int:
+        # split the dates to month and day.
+        arriveAliceMonth, arriveAliceDay = map(int, arriveAlice.split("-"))
+        leaveAliceMonth, leaveAliceDay = map(int, leaveAlice.split("-"))
+        arriveBobMonth, arriveBobDay = map(int, arriveBob.split("-"))
+        leaveBobMonth, leaveBobDay = map(int, leaveBob.split("-"))
+
+        # prefixOfCalendar : initialize the calendar and in the past we will use this to convert month to day, index is 1 - based
+        # spentTogether, aliceSpent : work as cache list. and index is 1 - based
+        calendar = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
+        prefixOfCalendar = [0] * 13
+        totalDates = sum(calendar)
+        spentTogether, aliceSpent = [0] * (totalDates + 1), [0] * (totalDates + 1)
+
+        # calculate the prefix of calendar
+        for i in range(1, len(calendar)):
+            prefixOfCalendar[i] = prefixOfCalendar[i - 1] + calendar[i]
+
+        # if the string is "01-15", it can be treat as 15 days.
+        # if the string is "02-27", it can be treat as 58 days.
+        # So, it can be "prefixOfCalendar[month - 1] + day"
+        # and in the problem it includes the leaveDate so +1 need to be in .
+        arriveAliceTotal = prefixOfCalendar[arriveAliceMonth - 1] + arriveAliceDay
+        leaveAliceTotal = prefixOfCalendar[leaveAliceMonth - 1] + leaveAliceDay
+        for i in range(arriveAliceTotal, leaveAliceTotal + 1):
+            aliceSpent[i] += 1
+
+        # check the aliceSpent[i] is True.
+        # if it is, they spentTogether is True too.
+        arriveBobTotal = prefixOfCalendar[arriveBobMonth - 1] + arriveBobDay
+        leaveBobTotal = prefixOfCalendar[leaveBobMonth - 1] + leaveBobDay
+        for i in range(arriveBobTotal, leaveBobTotal + 1):
+            if aliceSpent[i]:
+                spentTogether[i] += 1
+
+        # I used list because of this sum function.
+        return sum(spentTogether)