v0.40: Create exercises. Challenge the community.

prefix_sum

Your mission

Write a function that fills a separate output buffer with the running totals of an integer array, one total per element.

See it in action

int a[] = {1, 2, 3}; long out[3]; prefix_sum(a, 3, out);

Expected result

1 3 6

Your checklist

For your own tracking. Tests grade your code.

a points to the n integers to read, and out points to a buffer with room for n values of type long.
Set out[i] to the sum of a[0] through a[i] included, so out[0] equals a[0] and out[i] equals out[i - 1] + a[i].
Write exactly n values into out, never more.
Treat a as read-only. Never write through it.
When n is 0, leave out untouched and return.
The output type is long because the running total can outgrow an int even when every single element fits in one. Widen to long before you add, not after.
The checker prints the values of out on one line, separated by a single space, with a trailing newline.

More examples

int a[] = {5, -2, 7, -10}; long out[4]; prefix_sum(a, 4, out);

Expected result

5 3 10 0

int a[] = {2000000000, 2000000000, 2000000000}; long out[3]; prefix_sum(a, 3, out);

Expected result

2000000000 4000000000 6000000000

int a[] = {10, 20, 30, 40}; long out[4] = {-7, -7, -7, -7}; prefix_sum(a, 2, out);

Expected result

10 30 -7 -7

int a[] = {7, 8, 9}; long out[3] = {-1, -1, -1}; prefix_sum(a, 0, out);

Expected result

-1 -1 -1

Constraints

Expected files

prefix_sum.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

prefix_sum

Arrays and matrices

Your mission

Write a function that fills a separate output buffer with the running totals of an integer array, one total per element.

See it in action

int a[] = {1, 2, 3}; long out[3]; prefix_sum(a, 3, out);

Expected result

1 3 6

Your checklist

For your own tracking. Tests grade your code.

a points to the n integers to read, and out points to a buffer with room for n values of type long.
Set out[i] to the sum of a[0] through a[i] included, so out[0] equals a[0] and out[i] equals out[i - 1] + a[i].
Write exactly n values into out, never more.
Treat a as read-only. Never write through it.
When n is 0, leave out untouched and return.
The output type is long because the running total can outgrow an int even when every single element fits in one. Widen to long before you add, not after.
The checker prints the values of out on one line, separated by a single space, with a trailing newline.

More examples

int a[] = {5, -2, 7, -10}; long out[4]; prefix_sum(a, 4, out);

Expected result

5 3 10 0

int a[] = {2000000000, 2000000000, 2000000000}; long out[3]; prefix_sum(a, 3, out);

Expected result

2000000000 4000000000 6000000000

int a[] = {10, 20, 30, 40}; long out[4] = {-7, -7, -7, -7}; prefix_sum(a, 2, out);

Expected result

10 30 -7 -7

int a[] = {7, 8, 9}; long out[3] = {-1, -1, -1}; prefix_sum(a, 0, out);

Expected result

-1 -1 -1

Constraints

Expected files

prefix_sum.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

Tests

Run the tests to grade your code

Build your code, then check each test here. Open a result to inspect its output.

Build

01Running totals of three positivesWaiting

02Single element copies straight throughWaiting

03Length zero leaves out untouchedWaiting

04Only the first n slots are writtenWaiting

05Negative values pull the total back downWaiting

06All negative valuesWaiting

07Only zerosWaiting

08Alternating plus and minusWaiting

09Eight elementsWaiting

10Total climbs past INT_MAXWaiting

11INT_MAX twice, then back under with INT_MINWaiting

12Total drops below INT_MINWaiting

13The input array is left as it wasWaiting

prefix_sum

Your mission

Write a function that fills a separate output buffer with the running totals of an integer array, one total per element.

See it in action

int a[] = {1, 2, 3}; long out[3]; prefix_sum(a, 3, out);

Expected result

1 3 6

Your checklist

For your own tracking. Tests grade your code.

a points to the n integers to read, and out points to a buffer with room for n values of type long.
Set out[i] to the sum of a[0] through a[i] included, so out[0] equals a[0] and out[i] equals out[i - 1] + a[i].
Write exactly n values into out, never more.
Treat a as read-only. Never write through it.
When n is 0, leave out untouched and return.
The output type is long because the running total can outgrow an int even when every single element fits in one. Widen to long before you add, not after.
The checker prints the values of out on one line, separated by a single space, with a trailing newline.

More examples

int a[] = {5, -2, 7, -10}; long out[4]; prefix_sum(a, 4, out);

Expected result

5 3 10 0

int a[] = {2000000000, 2000000000, 2000000000}; long out[3]; prefix_sum(a, 3, out);

Expected result

2000000000 4000000000 6000000000

int a[] = {10, 20, 30, 40}; long out[4] = {-7, -7, -7, -7}; prefix_sum(a, 2, out);

Expected result

10 30 -7 -7

int a[] = {7, 8, 9}; long out[3] = {-1, -1, -1}; prefix_sum(a, 0, out);

Expected result

-1 -1 -1

Constraints

Expected files

prefix_sum.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

v0.40: Create exercises. Challenge the community.

Meet Studio →

prefix_sum

Arrays and matrices

Your mission

Write a function that fills a separate output buffer with the running totals of an integer array, one total per element.

See it in action

int a[] = {1, 2, 3}; long out[3]; prefix_sum(a, 3, out);

Expected result

1 3 6

Your checklist

For your own tracking. Tests grade your code.

a points to the n integers to read, and out points to a buffer with room for n values of type long.
Set out[i] to the sum of a[0] through a[i] included, so out[0] equals a[0] and out[i] equals out[i - 1] + a[i].
Write exactly n values into out, never more.
Treat a as read-only. Never write through it.
When n is 0, leave out untouched and return.
The output type is long because the running total can outgrow an int even when every single element fits in one. Widen to long before you add, not after.
The checker prints the values of out on one line, separated by a single space, with a trailing newline.

More examples

int a[] = {5, -2, 7, -10}; long out[4]; prefix_sum(a, 4, out);

Expected result

5 3 10 0

int a[] = {2000000000, 2000000000, 2000000000}; long out[3]; prefix_sum(a, 3, out);

Expected result

2000000000 4000000000 6000000000

int a[] = {10, 20, 30, 40}; long out[4] = {-7, -7, -7, -7}; prefix_sum(a, 2, out);

Expected result

10 30 -7 -7

int a[] = {7, 8, 9}; long out[3] = {-1, -1, -1}; prefix_sum(a, 0, out);

Expected result

-1 -1 -1

Constraints

Expected files

prefix_sum.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

Tests

Run the tests to grade your code

Build your code, then check each test here. Open a result to inspect its output.

Build

01Running totals of three positivesWaiting

02Single element copies straight throughWaiting

03Length zero leaves out untouchedWaiting

04Only the first n slots are writtenWaiting

05Negative values pull the total back downWaiting

06All negative valuesWaiting

07Only zerosWaiting

08Alternating plus and minusWaiting

09Eight elementsWaiting

10Total climbs past INT_MAXWaiting

11INT_MAX twice, then back under with INT_MINWaiting

12Total drops below INT_MINWaiting

13The input array is left as it wasWaiting