178. Design Digital Wellbeing System to Track App Screen Usage

Design a Digital Wellbeing System to Track Screen Usage of Apps

You need to design a DigitalWellbeingSystem that keeps track of screen usage for different applications.

The system receives usage records for apps. Each usage record contains an app name, a day number, and the amount of screen time used on that day.

The system should allow querying usage statistics for applications.

The system only stores data for the most recent 7 days based on the latest day seen by the system. Older data must be removed automatically.

Day values passed to addUsage will be monotonic non-decreasing across all addUsage calls on the same object.

Method Signature

Initialize

DigitalWellbeingSystem()

Creates a new empty object of the digital wellbeing system.

Add Usage

void addUsage(String appName, int day, int minutes)

appName is the name of the application.
day is an integer representing the day number.
minutes is the screen time used by the application on that day.
Across all calls to addUsage on the same object, day values will be monotonic non-decreasing.
If the same app receives multiple usage records for the same day, add all minutes together.
After adding usage, keep only data from the most recent 7 days based on the latest day seen so far.

Get App Usage

int getAppUsage(String appName, int day)

Returns the total usage in minutes for appName on the given day.
Returns 0 if the app has no stored usage for that day.
Returns 0 if the requested day is outside the stored last 7 days.

Get Total Usage

int getTotalUsage(int day)

Returns the total screen time in minutes across all apps for the given day.
Returns 0 if there is no stored usage for that day.
Returns 0 if the requested day is outside the stored last 7 days.

Get Usage Statistics

List<String> getUsageStatistics()

Returns usage statistics for all stored app-day pairs.
Each string must be formatted as "day,appName,minutes".
The result must be sorted by day in increasing order.
If two records have the same day, sort them by appName in lexicographical order.
Lexicographical order is case-sensitive.
Only data from the stored last 7 days should be returned.

Retention Rule

Let latestDay be the greatest day value passed to addUsage so far for the current object. The system should only keep usage data where:

latestDay - 6 ≤ day ≤ latestDay

Day Order Rule

Day values in addUsage calls are monotonic non-decreasing. This means each new addUsage call will have a day value greater than or equal to the previous addUsage call's day value for the same object. Query methods may request any day value.

Constraints

1 ≤ appName.length() ≤ 50
appName contains lowercase letters, uppercase letters, digits, spaces, hyphens, or underscores.
1 ≤ day ≤ 10^9
1 ≤ minutes ≤ 1440
At most 10^5 calls will be made in total.
Parameter values will never be null.

Examples

Example 1

DigitalWellbeingSystem system = new DigitalWellbeingSystem()
system.addUsage(appName = "ChatApp", day = 10, minutes = 40)
system.addUsage(appName = "VideoApp", day = 10, minutes = 90)
system.addUsage(appName = "ChatApp", day = 10, minutes = 15)
system.getAppUsage(appName = "ChatApp", day = 10)
Output: 55
system.getTotalUsage(day = 10)
Output: 145
system.getUsageStatistics()
Output: ["10,ChatApp,55", "10,VideoApp,90"]

Example 2

DigitalWellbeingSystem system = new DigitalWellbeingSystem()
system.addUsage(appName = "Browser", day = 3, minutes = 25)
system.addUsage(appName = "Music", day = 4, minutes = 70)
system.addUsage(appName = "Browser", day = 9, minutes = 35)
Since the latest day is 9, only days from 3 to 9 are stored.
system.getAppUsage(appName = "Browser", day = 3)
Output: 25
system.addUsage(appName = "Game", day = 10, minutes = 120)
Since the latest day is now 10, only days from 4 to 10 are stored.
system.getAppUsage(appName = "Browser", day = 3)
Output: 0
system.getUsageStatistics()
Output: ["4,Music,70", "9,Browser,35", "10,Game,120"]

Example 3

DigitalWellbeingSystem system = new DigitalWellbeingSystem()
system.addUsage(appName = "Mail", day = 20, minutes = 45)
system.addUsage(appName = "Mail", day = 21, minutes = 30)
system.addUsage(appName = "Calendar", day = 21, minutes = 15)
system.getAppUsage(appName = "Mail", day = 20)
Output: 45
system.getTotalUsage(day = 21)
Output: 45
system.getUsageStatistics()
Output: ["20,Mail,45", "21,Calendar,15", "21,Mail,30"]

Example 4

DigitalWellbeingSystem system = new DigitalWellbeingSystem()
system.addUsage(appName = "A", day = 1, minutes = 10)
system.addUsage(appName = "B", day = 2, minutes = 20)
system.addUsage(appName = "C", day = 7, minutes = 30)
system.addUsage(appName = "D", day = 8, minutes = 40)
Since the latest day is 8, only days from 2 to 8 are stored.
system.getTotalUsage(day = 1)
Output: 0
system.getTotalUsage(day = 2)
Output: 20
system.getUsageStatistics()
Output: ["2,B,20", "7,C,30", "8,D,40"]