Google Hash Code 2021 practice problem solution: Even More Pizza

Problem statement

Algorithm description:

• Phase 1: Build a solution
• Phase 2: Optimizations

Phase 1 - Build a solution

1. Sort pizzas by number of ingredients.
2. Build deliveries, first teams of 4, after that 3, after that 2:
   2.1 Select the pizza with the most ingredients.
   2.2 Select the pizza that will give the best improvement in delivery (most new ingredients, with the least overlapping ingredients).
   2.3 Repeat 2.2 until the delivery is ready.

Phase 2 - Optimization

1. Try to swap 2 pizzas between any 2 deliveries - if it improves the score, make the swap.
2. Try to swap 1 pizza between any 2 deliveries - if it improves the score, make the swap.
3. Try to swap a pizza from any delivery with unused pizza - if it improves the score, make the swap.
4. Try to move 1 pizza between 2 deliveries (# of pizza in the 2 deliveries must be -+1) - if it improves the score, make the swap.
5. If any improvement performed in 1-4 - go to 1

Notes

1. Phase 1 takes about 5 seconds to run.
2. Phase 2 takes about 50 minutes to run with the current restrictions (implemented for D & E which are huge). About 1% score improvement.

Scores

Input	Phase 1	Phase 1 + 2
A – Example	74	74
B – A little bit of everything	12,922	13,533
C – Many ingredients	706,624,572	712,692,751
D – Many pizzas	7,863,102	7,911,296
E – Many teams	10,789,627	10,837,821
Total	725,290,297	731,455,475