chore: day 21

Easy/Day 21/problem.txt

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+Alice shuffled a set of cards, each containing a number from 1 to n, with four cards for each number.
+After removing one card, she handed you the remaining stack. The i-th card in the stack (where i ranges from 1 to 4n−1) has a number Ai written on it.
+Your task is to determine which number Alice took from the original set.
+
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------
+
+Input:
+First line of input contains an integer n (1 <= n <= 10^5).
+Second line of input conatains 4n-1 integers.
+
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------
+
+Output:
+Print the missing number.
+
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------
+
+Time Limit: 2 sec
+Memory Limit: 1024 MB

Easy/Day 21/sample_tc.txt

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+Sample Input 1:
+3
+1 3 2 3 3 2 2 1 1 1 2
+
+Sample Output 1:
+3
+
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------
+
+Sample Input 2:
+1
+1 1 1
+
+Sample Output 2:
+1
+
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------
+
+Sample Input 3:
+4
+3 2 1 1 2 4 4 4 4 3 1 3 2 1 3
+
+Sample Output 3:
+2

Easy/Day 21/solution.cpp

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+// Write your code here.