Improved matchmaking performance

[Ratio2]

The order of combinations has changed slightly. Now the result is sorted according to the sorting of the input data.

Before these changes, matchmaking with override is very slow with more than 30 players:
players - time in seconds
10 - 1.1
20 - 1.9
22 - 2
24 - 2
26 - 3
28 - 8
30 - 28
32 - 118

[CLAassistant]

All committers have signed the CLA.

[sesposito]

Hello @Ratio2, can you elaborate a bit more on what this PR is doing to improve performance?

[Ratio2]

Hello @Ratio2, can you elaborate a bit more on what this PR is doing to improve performance?

Input data:
func combineIndexes(from []*MatchmakerIndex, min, max int)
len(from) = 32
min = 2
max = 2

The function call duration is 118 seconds, since we have complexity O(N*2^N) from the input array size regardless of min/max. The loop for combinationBits := 1; combinationBits < (1 << length); combinationBits++ consists of 2^32 iterations, which is a lot, and there is also an inner loop for element := uint(0); element < length; element++.

The main idea of ​​the change is to not iterate over impossible combinations in the loop. If max = 2, then we are not interested in combinations of 3 or more elements.

iterium.Combinations generates all possible combinations of N elements.
rangeCombinations generates all possible combinations of 1..N elements. If the input is [a, b, c], then the output is [[a], [a, b], [a, c], [b], [b, c], [c]].

[rbrewer-echelon]

Suggested change

	// Merge a slide into a string.
	// Merge a slice into a string.