Find the Missing Number

The array {1, 2, 4, 5, 6} should contain the numbers 1 through 6, but exactly one is missing. Find and print the missing number:

3

The full sum of 1 through 6 is 21. Subtract the actual array sum from that to find the gap. Use the formula n * (n + 1) / 2 with n = 6.

Expected Output:

Topics:

Arrays

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