Lunchtime Diary, Entry Number 30 – The November Lunchtime

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November is a busy month – with the school term reaching its busiest peak and a constant downpour of homework before winter break arrives. I daresay the Lunchtime 2015 held on the 29th of November was affected by this yearly phenomena with the number of participants lower than usual. The ones who did participate had a competitive problem set to go up against which included Black And White Cells, Query over Matrix, Product on Tree and Chef And A Complete Graph. The problem setters for the contest were Amit Pandey and Sunny Aggarwal, problem tester – Pushkar Mishra and the editorialist Prateek Gupta.

Here are a few statistics for a brief view of the contest.

  • Total Users: 559
  • Total Submissions: 2925
  • Number of distinct users with correct submissions: 434
  • Total users from India: 303
  • Total users not from India: 256

The problems for the contest proved to be on two ends of the difficulty spectrum. Some saw a hoard of submissions while some went hardly attempted. Read on to see how our users fared against these obstacles in their race to the top.

Obstacle 1:

Black And White Cells

  • Number of submissions with 100 points = 360
  • Number  of submissions with 70 points = 1
  • Number  of submissions with 60 points = 1
  • Number  of submissions with 30 points = 6

Score: BWCELL-0 USER-1

Obstacle 2:

Query over Matrix

  • Number of submissions with 100 points = 172
  • Number  of submissions with 20 points = 135


Obstacle 3:

Product on Tree

  • Number of submissions with 100 points = 17
  • Number  of submissions with 40 points = 5
  • Number  of submissions with 20 points = 25


Obstacle 4:

Chef And A Complete Graph

  • Number of submissions with 100 points = 7
  • Number  of submissions with 25 points = 23


With a score of 2-2 the November Lunchtime ended with a tie between the problems and the participants. Watch this space for the score next month and see if the participants beat the problems or do the problems take them down.

Meanwhile, take a look at the top performers of November Lunchtime ‘15.


Rest of the World:

  • fataleagle – Don Mills Collegiate Institute
  • kmcode – Omori 7th Junior High School
  • ptnk131627 – VNU-HCM High School for the Gifted Vietnam
  • akali – Issyk Kazakh – Turkish High School
  • kozhakhmetoff – Issyk Kazakh – Turkish High School
  • bayram98tm – Bashkent Turkmen-Turkish High School
  • hafiz_00 – Issyk Kazakh – Turkish High School
  • bekmyrat – Bashkent Turkmen-Turkish High School
  • mrkerim – Bashkent Turkmen-Turkish High School
  • msaska9 – Fazekas Mihály Gimnázium

For a detailed explanation of the solutions, find the editorials at:

We hope to see you at the contests.

Over and Out,
Team CodeChef

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