Bulls N Cows

The code-breaking mind game of Bulls & Cows, where you need to guess a 4 digit number.

Android decides a 4 digit secret number (digits could be repeated and the number may start with zeroes) and you need to guess this 4 digit number with the help of bulls and cows. Take a guess, enter a 4 digit number and Android will tell you how many bulls and cows exist in your guess.

What is a bull? If a correct digit exists in your guess and it is in the correct position in the number, then it is a bull.

What is a cow? If a correct digit exists but not in its correct position, then it is a cow.

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Example 1:

Secret number - 5731

Your guess - 5678

Bulls = 1 (The digit 5 is at its correct position)
Cows = 1 (The digit 7 exists in the secret number but not at its correct position)

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Example 2:

Secret number - 0409

Your guess - 1904

Bulls = 1 (The digit 0 is at its correct position)
Cows = 2 (The digits 4 & 9 exist in the secret number but not at their correct positions)

Note: 0 in the above guess is only shown as a Bull since it was matched to a bull first. If your guess had 2 zeros, it would match both.
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The idea therefore is to have 4 Bulls and 0 Cows (all 4 digits in the correct positions)

Learn from each of your guesses and arrive at the secret number! You have 10 chances to find the secret number!

Happy playing!