Without additional variables, or special casing the last range: 
my @ranges = map {[int($_*($M+1)/$N), int(($_+1)*(($M+1)/$N))-1]} 0..$
+N - 1;

[download]
All the ranges should differ at most 1 in size.

In reply to Re: Split range 0 to M into N non-overlapping (roughly equal) ranges. by JavaFan
in thread Split range 0 to M into N non-overlapping (roughly equal) ranges. by BrowserUk

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