Checking if a row of a 2-dimensional array exists anywhere within another array

Question

Say I have the following sorted array:

int[] numbers = {0, 0, 1, 2, 2, 2} .

How can I check if any sub-array of length 3 of numbers exists in the following 2-dimensional array:

int[][] sets = { {0, 0, 0}, {1, 1, 1}, {2, 2, 2} }

In this simple example, the last 3 elements of numbers are clearly contained as an array in sets , but in my actual program, sets will have far more 3 digit permutations of more numbers, but they will all remain length 3, and numbers will always be sorted.

Answer 1

If only the numbers less than ten are allowed, you have up to 1000 possible sequences of three numbers. Encode them as 100*a _i +10*a _i+1 +a _i+2 , and store the index of the first such sequence in a 1001-element array.

In your case numbers would be translated into

0, 0, 1, 2, 2, 2

  1 - 0
 12 - 1
122 - 2
222 - 3

The first column is the index into 1001-element array; the second column is the value that gets placed at that index. The remaining positions of the 1001-element array are set to -1.

To see if numbers contain a three-element sequence construct 100*s ₀ +10*s ₁ +s ₂ number from them, and look it up in the 1001-element array. If you get -1, the sequence is not there; otherwise, you would get the starting index of the desired subsequence.