freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-391-hopping-game.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
5900f4f31000cf542c510006	Problem 391: Hopping Game	5	302056	problem-391-hopping-game

--description--

Let sk be the number of 1’s when writing the numbers from 0 to k in binary.

For example, writing 0 to 5 in binary, we have 0, 1, 10, 11, 100, 101. There are seven 1’s, so s5 = 7.

The sequence S = {sk : k ≥ 0} starts {0, 1, 2, 4, 5, 7, 9, 12, ...}.

A game is played by two players. Before the game starts, a number n is chosen. A counter c starts at 0. At each turn, the player chooses a number from 1 to n (inclusive) and increases c by that number. The resulting value of c must be a member of S. If there are no more valid moves, the player loses.

For example: Let n = 5. c starts at 0. Player 1 chooses 4, so c becomes 0 + 4 = 4. Player 2 chooses 5, so c becomes 4 + 5 = 9. Player 1 chooses 3, so c becomes 9 + 3 = 12. etc. Note that c must always belong to S, and each player can increase c by at most n.

Let M(n) be the highest number the first player can choose at her first turn to force a win, and M(n) = 0 if there is no such move. For example, M(2) = 2, M(7) = 1 and M(20) = 4.

Given Σ(M(n))3 = 8150 for 1 ≤ n ≤ 20.

Find Σ(M(n))3 for 1 ≤ n ≤ 1000.

--hints--

euler391() should return 61029882288.

assert.strictEqual(euler391(), 61029882288);

--seed--

--seed-contents--

function euler391() {

  return true;
}

euler391();

--solutions--

// solution required