299. Bulls and Cows #

Problem #

You are playing the Bulls and Cows game with your friend.

You write down a secret number and ask your friend to guess what the number is. When your friend makes a guess, you provide a hint with the following info:

The number of “bulls”, which are digits in the guess that are in the correct position. The number of “cows”, which are digits in the guess that are in your secret number but are located in the wrong position. Specifically, the non-bull digits in the guess that could be rearranged such that they become bulls. Given the secret number secret and your friend’s guess guess, return the hint for your friend’s guess.

The hint should be formatted as “xAyB”, where x is the number of bulls and y is the number of cows. Note that both secret and guess may contain duplicate digits.

Example 1:

Input: secret = "1807", guess = "7810"
Output: "1A3B"
Explanation: Bulls are connected with a '|' and cows are underlined:
"1807"
  |
"7810"

Example 2:

Input: secret = "1123", guess = "0111"
Output: "1A1B"
Explanation: Bulls are connected with a '|' and cows are underlined:
"1123"        "1123"
  |      or     |
"0111"        "0111"
Note that only one of the two unmatched 1s is counted as a cow since the non-bull digits can only be rearranged to allow one 1 to be a bull.

Example 3:

Input: secret = "1", guess = "0"
Output: "0A0B"

Example 4:

Input: secret = "1", guess = "1"
Output: "1A0B"

Constraints:

• 1 <= secret.length, guess.length <= 1000
• secret.length == guess.length
• secret and guess consist of digits only.

Problem Summary #

You are playing the Bulls and Cows game with your friend. The rules of the game are as follows:

Write down a secret number and ask your friend to guess what the number is. Each time your friend makes a guess, you give him a hint containing the following information:

How many digits in the guess have both the correct digit and the correct position (called “Bulls”), and how many digits have the correct digit but are in the wrong position (called “Cows”). In other words, how many non-bull digits in this guess can be rearranged to become bull digits. Given the secret number secret and your friend’s guessed number guess, return the hint for your friend’s guess.

The hint format is “xAyB”, where x is the number of bulls, y is the number of cows, A represents bulls, and B represents cows.

Note that both the secret number and your friend’s guessed number may contain duplicate digits.

Solution Approach #

• Count the number of positions where the indices match and the corresponding elements are the same, which is x
• Remove the x bull elements from secret and guess respectively; the number of common elements remaining in secret and guess is y
• Convert x and y to strings, concatenate them with “A” and “B” respectively, and return the result

Code #

package leetcode

import "strconv"

func getHint(secret string, guess string) string {
	cntA, cntB := 0, 0
	mpS := make(map[byte]int)
	var strG []byte
	n := len(secret)
	var ans string
	for i := 0; i < n; i++ {
		if secret[i] == guess[i] {
			cntA++
		} else {
			mpS[secret[i]] += 1
			strG = append(strG, guess[i])
		}
	}
	for _, v := range strG {
		if _, ok := mpS[v]; ok {
			if mpS[v] > 1 {
				mpS[v] -= 1
			} else {
				delete(mpS, v)
			}
			cntB++
		}
	}
	ans += strconv.Itoa(cntA) + "A" + strconv.Itoa(cntB) + "B"
	return ans
}