Window length is right minus left plus one
Updated
Length = R - L + 1 when L ≤ R. Count the cells, inclusive both ends. Do not count the gap between the edges.
What to focus on
Inclusive length is R-L+1. Exclusive-right [L,R) would be R-L. Mixing the two is the off-by-one.
Worked examples
three cells
a = [4, 1, 9, 1], L=1 R=3- R-L+1 = 3-1+1 = 3
- indices 1,2,3
Result: length 3
one cell
a = [7], L=0 R=0- 0-0+1 = 1
- the single index 0
Result: length 1
string window
s = "abca", L=0 R=2- 2-0+1 = 3
- chars a,b,c
Result: length 3
Try it
Write length(L, R). L is the left index. R is the right index with L ≤ R. The window includes both ends, so length is R-L+1. Return R-L+1. Contrast exclusive [0, 3) on n=4, which has length 3 not 4. On a=[4, 1, 9, 1] (1, 3); a=[7] (0, 0); s="abca" (0, 2).
a (or s) is nonempty. L ≤ R.