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package corpus
import (
"math/rand"
"testing"
)
func naivePrefixSum(a []int64, r int) int64 {
var s int64
for i := 1; i <= r; i++ {
s += a[i]
}
return s
}
func TestFenwickBasic(t *testing.T) {
var ft fenwikTree
values := []int64{0, 5, -3, 7, 10}
for _, v := range values[1:] {
ft.addNew(v)
}
if ft.size != len(values)-1 {
t.Fatalf("size mismatch: got %d want %d", ft.size, len(values)-1)
}
for i := 1; i < ft.size; i++ {
got := ft.prefixSumTo(i)
want := naivePrefixSum(values, i)
if got != want {
t.Fatalf("prefixSumTo(%d) = %d, want %d", i, got, want)
}
}
}
func TestFenwickExtend(t *testing.T) {
var ft fenwikTree
n := 1000
ref := make([]int64, 1)
for i := 1; i <= n; i++ {
ft.addNew(int64(i))
ref = append(ref, int64(i))
if ft.prefixSumTo(i) != naivePrefixSum(ref, i) {
t.Fatalf("extend failed at i=%d, fw=%d and naive=%d", i, ft.prefixSumTo(i), naivePrefixSum(ref, i))
}
}
}
func TestFenwickRandom(t *testing.T) {
var ft fenwikTree
ft.extendAndRebuild()
ref := make([]int64, 1)
rng := rand.New(rand.NewSource(1))
for step := range 10_000 {
if rng.Intn(2) == 0 || ft.size <= 2 {
v := int64(rng.Intn(1000) - 500)
ft.addNew(v)
ref = append(ref, v)
} else {
i := rng.Intn(ft.size-1) + 1
v := int64(rng.Intn(1000) - 500)
ft.add(i, v)
ref[i] += v
}
i := rng.Intn(ft.size)
if ft.prefixSumTo(i) != naivePrefixSum(ref, i) {
t.Fatalf("mismatch at step %d, i=%d", step, i)
}
if ft.prefixSumTo(ft.size) != ft.fullSum {
t.Fatalf("fullSum mismatch %d, sm=%d, fullSum=%d, naive=%d", step, ft.prefixSumTo(ft.size), ft.fullSum, naivePrefixSum(ref, ft.size))
}
}
}
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