## CCC '10 J5 - Knight Hop

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Points: 7
Time limit: 1.0s
Memory limit: 64M

Problem type
##### Canadian Computing Competition: 2010 Stage 1, Junior #5

Below is an chessboard on which we will designate square locations using the ordered pairs as indicated. For example, notice that piece is at position and piece is at position .

8 7 ~B~ ~A~

A knight is a special game piece that can leap over other pieces, moving in the "L" pattern. Specifically, in the diagram below, represents the knight's starting position and the numbers 1 through 8 represent possible places the knight may move to.

8 7 6 5 4 8 1 7 2 ~K~ 6 3 5 4

Your program will read the starting location of the knight and output the smallest number of jumps or moves needed to arrive at a location specified in the second input.

#### Input Specification

Your program will read four integers, where each integer is in the range . The first two integers represent the starting position of the knight. The second two integers represent the final position of the knight.

#### Output Specification

Your program should output the minimum (non-negative integer) number of moves required to move the knight from the starting position to the final position. Note that the knight is not allowed to move off the board during the sequence of moves.

#### Sample Input 1

2 1
3 3

#### Output for Sample Input 1

1

#### Sample Input 2

4 2
7 5

#### Output for Sample Input 2

2

• commented on Aug. 25, 2022, 4:54 p.m.

Help guys. What I have to learn to solve this problem? I think I don't have the bases to solve it.

• commented on Aug. 25, 2022, 7:22 p.m.

The problem type is graph theory. So... I guess you need to learn graph theory.

• commented on Aug. 26, 2022, 1:39 p.m.

Or you can brute force it.

• commented on Nov. 28, 2020, 1:34 p.m.

A chess knight will take at most 5 moves to reach a given square. I don't know if that bit of chess knowledge can be helpful for this problem.

• commented on Jan. 17, 2022, 5:05 p.m.

My brain after reading this: to lazy too implement resursion copy-pastes the same code 6 times >_<

• commented on April 18, 2021, 11:06 p.m.

Good to know I won't need to make a recursion that loops like 50 times without TLE.

• commented on Dec. 11, 2020, 11:31 a.m.

It's actually 6 in some cases, such as from corner to corner.

• commented on Jan. 8, 2021, 8:29 p.m.

Ah right, it is 6 moves. Sorry.

• commented on Dec. 1, 2020, 12:36 a.m.

This comment is hidden due to too much negative feedback. Show it anyway.

• commented on Dec. 1, 2020, 9:29 p.m.

I was thinking you could pass the problem by setting an exit condition on recursion to be 5, instead of using a visited cache which is what I assume the problem intended.

• commented on June 15, 2020, 3:44 p.m. edited

Using std::queue with pair<int,int>: https://dmoj.ca/submission/2145895 still MLE's.

Edit: For comment below.

• commented on June 23, 2021, 5:03 p.m.

I believe I did the same thing and my program passed without MLEing. I'm not sure why yours did not pass :(. https://dmoj.ca/src/3693845

• commented on June 29, 2021, 2:07 p.m.

If there was no memory limit their code would of TLE instead of MLE on test case #6 because of an infinite loop. See Jonathan's comment down below.

• commented on June 15, 2020, 3:52 p.m.

One mb ://

• commented on June 15, 2020, 12:32 p.m. edited

I mle by one mb on case 6 :(. Any optimization tips?

• commented on June 15, 2020, 1:58 p.m. edit 3

instead of making separate queues per dimension try using pairs to reduce the number of possible queue entries.

• commented on June 15, 2020, 3:51 p.m.

A queue of pair<int,int> still mle's. Maybe my BFS algorithm is inefficient? Best solutions only use like 1-2 mb.

• commented on June 15, 2020, 4:14 p.m. edit 2

Your program enters an infinite loop for the test case:

3 1
1 3
• commented on June 15, 2020, 4:33 p.m.

Thanks! I got it now!

• commented on June 15, 2020, 4:08 p.m.

Then it is most likely that you have a logical error/edge case you did not account for. The runtime for that case took abnormally long as well. I would advise you to look over the semantics.

• commented on June 15, 2020, 4:35 p.m. edit 3

"Then it is most likely that you have a logical error/edge case you did not account for."

You were right, I had if (visited.at(new_h).at(new_v) == 0) instead of if (visited.at(new_v).at(new_h) == 0).

*facepalm

Edit: edits were glitching idk why

• commented on May 7, 2020, 10:45 a.m.

Did the point total for this question decrease?? I recall this being worth 10 points.

• commented on May 8, 2020, 3:30 p.m.

Yes, the points rewarded for this problems was reduced from 10 points to 7 points to match the other classical graph theory problems.

• commented on May 8, 2020, 3:13 p.m.

I think

• commented on Feb. 9, 2019, 11:29 a.m.

What does IR mean and why do i get it when i submit

• commented on Aug. 1, 2017, 9:34 p.m.

wleung_bvg you're getting it too?

• commented on Aug. 2, 2017, 1:34 p.m. edited

Your code has variables that have indeterminate ("random") values. This can sometimes happen when declaring a variable in a non global scope without initializing it with a value. Simply initializing the boolean variable with the value false in your spot struct will allow your code to pass.

• commented on Aug. 2, 2017, 3:37 p.m.

Ah,thanks. Why does the first case work though?