Oliver Eyton-Williams ee1e8abd87

feat(curriculum): restore seed + solution to Chinese (#40683 )

* feat(tools): add seed/solution restore script

* chore(curriculum): remove empty sections' markers

* chore(curriculum): add seed + solution to Chinese

* chore: remove old formatter

* fix: update getChallenges

parse translated challenges separately, without reference to the source

* chore(curriculum): add dashedName to English

* chore(curriculum): add dashedName to Chinese

* refactor: remove unused challenge property 'name'

* fix: relax dashedName requirement

* fix: stray tag

Remove stray `pre` tag from challenge file.

Signed-off-by: nhcarrigan <nhcarrigan@gmail.com>

Co-authored-by: nhcarrigan <nhcarrigan@gmail.com>

2021-01-12 19:31:00 -07:00

2.6 KiB

Raw Blame History

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
5987fd532b954e0f21b5d3f6	Equilibrium index	5	302255	equilibrium-index

--description--

An equilibrium index of a sequence is an index into the sequence such that the sum of elements at lower indices is equal to the sum of elements at higher indices.

For example, in a sequence A:

$A_0 = -7$
$A_1 = 1$
$A_2 = 5$
$A_3 = 2$
$A_4 = -4$
$A_5 = 3$
$A_6 = 0$

3 is an equilibrium index, because:

$A_0 + A_1 + A_2 = A_4 + A_5 + A_6$

6 is also an equilibrium index, because:

$A_0 + A_1 + A_2 + A_3 + A_4 + A_5 = 0$

(sum of zero elements is zero)

7 is not an equilibrium index, because it is not a valid index of sequence A.

--instructions--

Write a function that, given a sequence, returns its equilibrium indices (if any).

Assume that the sequence may be very long.

--hints--

equilibrium should be a function.

assert(typeof equilibrium === 'function');

equilibrium([-7, 1, 5, 2, -4, 3, 0]) should return [3,6].

assert.deepEqual(equilibrium(equilibriumTests[0]), ans[0]);

equilibrium([2, 4, 6]) should return [].

assert.deepEqual(equilibrium(equilibriumTests[1]), ans[1]);

equilibrium([2, 9, 2]) should return [1].

assert.deepEqual(equilibrium(equilibriumTests[2]), ans[2]);

equilibrium([1, -1, 1, -1, 1, -1, 1]) should return [0,1,2,3,4,5,6].

assert.deepEqual(equilibrium(equilibriumTests[3]), ans[3]);

equilibrium([1]) should return [0].

assert.deepEqual(equilibrium(equilibriumTests[4]), ans[4]);

equilibrium([]) should return [].

assert.deepEqual(equilibrium(equilibriumTests[5]), ans[5]);

--seed--

--after-user-code--

const equilibriumTests =
  [[-7, 1, 5, 2, -4, 3, 0], // 3, 6
  [2, 4, 6], // empty
  [2, 9, 2], // 1
  [1, -1, 1, -1, 1, -1, 1], // 0,1,2,3,4,5,6
  [1], // 0
  [] // empty
  ];
const ans = [[3, 6], [], [1], [0, 1, 2, 3, 4, 5, 6], [0], []];

--seed-contents--

function equilibrium(a) {

}

--solutions--

function equilibrium(a) {
  let N = a.length,
    i,
    l = [],
    r = [],
    e = [];
  for (l[0] = a[0], r[N - 1] = a[N - 1], i = 1; i < N; i++)
    { l[i] = l[i - 1] + a[i], r[N - i - 1] = r[N - i] + a[N - i - 1]; }
  for (i = 0; i < N; i++)
    { if (l[i] === r[i]) e.push(i); }
  return e;
}

2.6 KiB Raw Blame History