## Friday, July 18, 2014

### Problem

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.

### Solution

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.
```public static class Result {
public int hits;
public int pseudoHits;
};

public static Result masterMind(String guess, String solution) {
Result res = new Result();
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;
}

//runner main
public static void main(String[] args) {
masterMind("YRGB", "RGGB");
}
```

Thanks.
References