giles
62712accdd
Some checks failed
Test, Build, and Deploy / test-build-deploy (push) Failing after 23s
Shoelace formula on a pentagon with integer vertices:
pts = [(0,0); (4,0); (4,3); (2,5); (0,3)]
2 * area = | Σ (x_i * y_{i+1} - x_{i+1} * y_i) |
= | 0*0 - 4*0 + 4*3 - 4*0 + 4*5 - 2*3 + 2*3 - 0*5
+ 0*0 - 0*3 |
= 32
Returns the doubled form (32) to stay integral.
Tests:
- let (x1, y1) = arr.(i) in -- tuple destructure from array
- arr.((i + 1) mod n) -- modular wrap-around index
- if a < 0 then - a else a -- prefix - negation
162 baseline programs total.
18 lines
368 B
OCaml
18 lines
368 B
OCaml
let pts = [(0, 0); (4, 0); (4, 3); (2, 5); (0, 3)]
|
|
|
|
let polygon_2area pts =
|
|
let arr = Array.of_list pts in
|
|
let n = Array.length arr in
|
|
let acc = ref 0 in
|
|
for i = 0 to n - 1 do
|
|
let (x1, y1) = arr.(i) in
|
|
let (x2, y2) = arr.((i + 1) mod n) in
|
|
acc := !acc + x1 * y2 - x2 * y1
|
|
done;
|
|
let a = !acc in
|
|
if a < 0 then - a else a
|
|
|
|
;;
|
|
|
|
polygon_2area pts
|