Three Moves Coding Interview Question | Skilled.dev
Interview Question

Three Moves

Write a function countTotalMoves that calculates the total ways to reach the last spot in a board using any combination of 1, 2, and 3 jumps. The input for the function is the length of the board.

You are developing a game where players can move 1, 2, or 3 steps. The board is a straight line, and you want to know the total number of ways you can reach the final spot for any combination of jumps.

When we say "total number of ways", we mean the count of all the possible unique paths you can take to reach the end by jumping 1, 2, or 3 spots from any point.

NOTE: If the board length is 0 or 1, you can assume it is 1 total way in both cases. This is an intentional decision by the interviewer which will allow you to focus on the logic of the solution. With a board length of 0, there is no board at all which is an edge case where the starting and ending location converge, so we'll say the total number of ways for the piece to exist in the game is still 1 which is not performing any jumps. With a board length of 1, the only combination of moves is using the 1-hop option. If we instead said for a board length of 0 that the total moves is 0, it complicates the base cases and doesn't really provide any additional meaning. There is an argument for length 0 to be either 0 or 1 moves with no "right answer", so we are opting for the simpler path.

const boardLength = 4;
countTotalMoves(boardLength);
// Answer: 7
// Ways to reach the end:
// 1,1,1,1
// 1,1,2
// 1,2,1
// 2,1,1
// 2,2
// 1,3
// 3,1
Board Length: 4
0
1
2
3
4

Breakdown

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Table of Contents

Validate My Answer

  1. A top-down approach is very elegant here. Think how to break this into subproblems and what your base cases would be.

  2. Ensure you handle all cases for negative, zero, and positive board lengths.

  3. There is a lot of repeated work for a brute force recursive solution. These are overlapping subproblems. Find a way to remove this to get a O(n) time and space solution.

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Table of Contents

Test Results

Run your code and see results here...

function countTotalMoves(boardLength) {
  // Your solution here
};
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Three Moves

Write a function countTotalMoves that calculates the total ways to reach the last spot in a board using any combination of 1, 2, and 3 jumps. The input for the function is the length of the board.

You are developing a game where players can move 1, 2, or 3 steps. The board is a straight line, and you want to know the total number of ways you can reach the final spot for any combination of jumps.

When we say "total number of ways", we mean the count of all the possible unique paths you can take to reach the end by jumping 1, 2, or 3 spots from any point.

NOTE: If the board length is 0 or 1, you can assume it is 1 total way in both cases. This is an intentional decision by the interviewer which will allow you to focus on the logic of the solution. With a board length of 0, there is no board at all which is an edge case where the starting and ending location converge, so we'll say the total number of ways for the piece to exist in the game is still 1 which is not performing any jumps. With a board length of 1, the only combination of moves is using the 1-hop option. If we instead said for a board length of 0 that the total moves is 0, it complicates the base cases and doesn't really provide any additional meaning. There is an argument for length 0 to be either 0 or 1 moves with no "right answer", so we are opting for the simpler path.

const boardLength = 4;
countTotalMoves(boardLength);
// Answer: 7
// Ways to reach the end:
// 1,1,1,1
// 1,1,2
// 1,2,1
// 2,1,1
// 2,2
// 1,3
// 3,1
Board Length: 4
0
1
2
3
4
function countTotalMoves(boardLength) {
  // Your solution here
};
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// Upgrade for full course access