[LeetCode] 299. Bulls and Cows

轉自LeetCode

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.

Solution

這題就是猜數字，然後給出幾Ａ幾Ｂ

用個 map 來記錄出現過的次數

• 如果數字被猜對了，就把 bulls 加 1

• 如果數字沒被猜對，檢查 map[secret[i]]，如果小於 0，代表該數字在 guess 有出現過，所以 cows 要加1，然後把 map[secret[i]] 減一

• 同理，如果數字沒被猜對，也要檢查 map[guess[i]]，如果大於 0，代表該數字在 secret 有出現過，所以 cows 要加1，然後把 map[guess[i]] 加一

kotlin