299. Bulls and Cows
Description
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.
Constraints:
1 <= secret.length, guess.length <= 1000
secret.length == guess.length
secret
andguess
consist of digits only.
Solutions
Solution 1: Counting
We create two counters, $cnt1$ and $cnt2$, to count the occurrence of each digit in the secret number and the friend's guess respectively. At the same time, we create a variable $x$ to count the number of bulls.
Then we iterate through the secret number and the friend's guess. If the current digit is the same, we increment $x$ by one. Otherwise, we increment the count of the current digit in the secret number and the friend's guess respectively.
Finally, we iterate through each digit in $cnt1$, take the minimum count of the current digit in $cnt1$ and $cnt2$, and add this minimum value to the variable $y$.
In the end, we return the values of $x$ and $y$.
The time complexity is $O(n)$, where $n$ is the length of the secret number and the friend's guess. The space complexity is $O(|\Sigma|)$, where $|\Sigma|$ is the size of the character set. In this problem, the character set is digits, so $|\Sigma| = 10$.
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