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.

**My initial thoughts:**

1st scan, we can find out how many hits there are by comparing character by character. During this scan, we can also build a hashtable for all the characters in the solution. The second scan, we count how many characters in the guess are matched in the hashtable. The counts – hints is the pseudo-hits.

**My initial codes:**

public static Pair<Integer> masterMind
(String guess, String solution) {
Hashtable<Character, Integer> table
= new Hashtable<Character, Integer>();
int hits = 0;
for (int i = 0; i < Math.min(solution.length(),
guess.length()); ++i) {
char charAtGuess = guess.charAt(i);
char charAtSol = solution.charAt(i);
table.put(charAtSol,
table.keySet().contains(charAtSol) ?
table.get(charAtSol) + 1 : 1);
if (charAtGuess == charAtSol)
hits++;
}
int counts = 0;
for (int i = 0; i < guess.length(); ++i) {
char charAtGuess = guess.charAt(i);
if (table.keySet().contains(charAtGuess)) {
counts++;
table.put(charAtGuess, table.get(charAtGuess) - 1);
if (table.get(charAtGuess) == 0)
table.remove(charAtGuess);
}
}
return new Pair<Integer>(hits, counts - hits);
}

**Solution**

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;
}

Comments:

My solution handles more general cases than the solution but the solution is more time and space efficient.

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