README_EN.md

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16.15. Master Mind

中文文档

Description

The Game of Master Mind is played as follows:

The computer has four slots, and each slot will contain a ball that is red (R). yellow (Y). green (G) or blue (B). For example, the computer might have RGGB (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:' Note that a slot that is a hit can never count as a pseudo-hit.

For example, if the actual solution is RGBY and you guess GGRR, you have one hit and one pseudo-hit. Write a method that, given a guess and a solution, returns the number of hits and pseudo-hits.

Given a sequence of colors solution, and a guess, write a method that return the number of hits and pseudo-hit answer, where answer[0] is the number of hits and answer[1] is the number of pseudo-hit.

Example:

Input:  solution="RGBY",guess="GGRR"
Output:  [1,1]
Explanation:  hit once, pseudo-hit once.

Note:

• len(solution) = len(guess) = 4
• There are only "R","G","B","Y" in solution and guess.

Solutions

Solution 1: Hash Table

We simultaneously traverse both strings, count the number of corresponding characters that are the same, and accumulate them in $x$. Then we record the characters and their frequencies in both strings in hash tables $cnt1$ and $cnt2$, respectively.

Next, we traverse both hash tables, count the number of common characters, and accumulate them in $y$. The answer is then $[x, y - x]$.

The time complexity is $O(C)$, and the space complexity is $O(C)$. Here, $C=4$ for this problem.

Python3

class Solution:
    def masterMind(self, solution: str, guess: str) -> List[int]:
        x = sum(a == b for a, b in zip(solution, guess))
        y = sum((Counter(solution) & Counter(guess)).values())
        return [x, y - x]

Java

class Solution {
    public int[] masterMind(String solution, String guess) {
        int x = 0, y = 0;
        Map<Character, Integer> cnt1 = new HashMap<>();
        Map<Character, Integer> cnt2 = new HashMap<>();
        for (int i = 0; i < 4; ++i) {
            char a = solution.charAt(i), b = guess.charAt(i);
            x += a == b ? 1 : 0;
            cnt1.merge(a, 1, Integer::sum);
            cnt2.merge(b, 1, Integer::sum);
        }
        for (char c : "RYGB".toCharArray()) {
            y += Math.min(cnt1.getOrDefault(c, 0), cnt2.getOrDefault(c, 0));
        }
        return new int[] {x, y - x};
    }
}

C++

class Solution {
public:
    vector<int> masterMind(string solution, string guess) {
        int x = 0, y = 0;
        unordered_map<char, int> cnt1;
        unordered_map<char, int> cnt2;
        for (int i = 0; i < 4; ++i) {
            x += solution[i] == guess[i];
            cnt1[solution[i]]++;
            cnt2[guess[i]]++;
        }
        for (char c : "RYGB") y += min(cnt1[c], cnt2[c]);
        return vector<int>{x, y - x};
    }
};

Go

func masterMind(solution string, guess string) []int {
	var x, y int
	cnt1 := map[byte]int{}
	cnt2 := map[byte]int{}
	for i := range solution {
		a, b := solution[i], guess[i]
		if a == b {
			x++
		}
		cnt1[a]++
		cnt2[b]++
	}
	for _, c := range []byte("RYGB") {
		y += min(cnt1[c], cnt2[c])
	}
	return []int{x, y - x}
}

JavaScript

/**
 * @param {string} solution
 * @param {string} guess
 * @return {number[]}
 */
var masterMind = function (solution, guess) {
    let counts1 = { R: 0, G: 0, B: 0, Y: 0 };
    let counts2 = { R: 0, G: 0, B: 0, Y: 0 };
    let res1 = 0;
    for (let i = 0; i < solution.length; i++) {
        let s1 = solution[i],
            s2 = guess[i];
        if (s1 === s2) {
            res1++;
        } else {
            counts1[s1] += 1;
            counts2[s2] += 1;
        }
    }
    let res2 = Object.keys(counts1).reduce((a, c) => a + Math.min(counts1[c], counts2[c]), 0);
    return [res1, res2];
};

Swift

class Solution {
    func masterMind(_ solution: String, _ guess: String) -> [Int] {
        var x = 0
        var y = 0
        var cnt1: [Character: Int] = [:]
        var cnt2: [Character: Int] = [:]

        for i in solution.indices {
            let a = solution[i]
            let b = guess[i]
            if a == b {
                x += 1
            }
            cnt1[a, default: 0] += 1
            cnt2[b, default: 0] += 1
        }

        let colors = "RYGB"
        for c in colors {
            let minCount = min(cnt1[c, default: 0], cnt2[c, default: 0])
            y += minCount
        }

        return [x, y - x]
    }
}