The Game of Master Mind is played as follows:
The computer has four slots containing balls that are red (R), yellow (Y), green (G) or blue (B).For example, the computer might have RGGB (e.g., Slot #1 is red, Slots #2 and #3 are green, Slot #4 is blue).
You, the user, are trying to guess the solution.You might, for example, guess YRGB.
When you guess the correct color for the correct slot, you get a “hit”.If you guess a color that exists but is in the wrong slot, you get a “pseudo-hit”.For example, the guess YRGB has 2 hits and one pseudo hit.
For each guess, you are told the number of hits and pseudo-hits.
Write a method that, given a guess and a solution, returns the number of hits and pseudo hits.
This problem is from Cracking the Coding interview. The book provides a very neat solution (shown below), except there is a bug in it. Consider a case where solution is "RGGB" and the guess is "GGGR", the code should return 2 hits and 1 pseudo hits, however, the solution gives us 2 hits and 2 pseudo hits. The reason is that the solution_mask only takes into account if there exists such character in the solution, so for the first "G", of course there exists another 2 Gs in the solution, but not in the correct position. However, in real time, we should taken into account the number of duplicate characters in the solution and the guess. I use a hashmap. My solution does need extra space. But since we only need at most 4 key, value pairs, it won't take too much extra space.
The solution provided by the book:
public static class Result { public int hits; public int pseudoHits; }; public static Result estimate(String guess, String solution) { Result res = new Result(); int solution_mask = 0; for (int i = 0; i < 4; ++i) { solution_mask |= 1 << (1 + solution.charAt(i) - ‘A’); } for (int i = 0; i < 4; ++i) { if (guess.charAt(i) == solution.charAt(i)) { ++res.hits; } else if ((solution_mask & (1 << (1 + guess.charAt(i) - ‘A’))) >= 1) { ++res.pseudoHits; } } return res; }
My solution:
import java.util.*; public class GameofMaster { private static class Result{ public int hits; public int pseudoHits; public Result(int hits, int pseudoHits){ this.hits = hits; this.pseudoHits = pseudoHits; } public String toString(){ return "hits: " + String.valueOf(hits) + "; pseudoHits: " + String.valueOf(pseudoHits); } } public static Result estimate(String guess, String solution){ Mapmap = new HashMap(); for (int i = 0; i < 4; i++){ char c = solution.charAt(i); if (!map.containsKey(c)) map.put(c, 1); else map.put(c, map.get(c) + 1); } int hits = 0; int pse = 0; for (int i = 0; i < 4; i++){ char c = guess.charAt(i); if (c == solution.charAt(i)){ hits++; if (!map.containsKey(c)) { pse--; continue; } map.put(c, map.get(c) - 1); if (map.get(c) == 0) map.remove(c); } else if (map.containsKey(c)) { pse++; map.put(c, map.get(c) - 1); if (map.get(c) == 0) map.remove(c); } } return new Result(hits, pse); } public static void main(String[] args) { System.out.println(estimate("RGGB", "RGGB").toString()); } }
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