# Question

Given an unsorted array of length N, a slice is defined as a pair of numbers (P, Q) so that:

- 0 <= P < Q <= N
- A[P], A[P+1]….A[Q] is arithmetic sequence
Example:

`input = { -1, 1, 3, 3, 3, 2, 1, 0 }`

Output 5 because there’re slices:

`(0, 2) (2, 4) (4, 6) (4, 7) (5, 7)`

# Solution

- count the length of arithmetic (countinuous) sequence
- form some slices
- proceed from the end of that sequence, till the end.

# Code

```
public int solve(int[] input) {
int len = input.length;
int p = 0;
int totalSlices = 0;
while (p + 1 < len) {
// check if there is a arithmetic sequence starting at p
// note that p is NOT the last element.
int diff = input[p + 1] - input[p];
int q = p + 1;
// starting from q, check arithmetic difference
while (q < len) {
if (input[q] - input[q - 1] == diff) {
q++;
} else {
break;
}
}
// so, the range [p, q-1] is a arithmetic sequence.
int seqLength = q - p;
if (seqLength >= 3) {
totalSlices += getSlicesCountFromArithmeticSeq(seqLength);
}
// update p (skip the range [p, q-1])
p = q - 1;
}
return totalSlices;
}
private int getSlicesCountFromArithmeticSeq(int k) {
// choose 2 from (k - 1)
return (k - 1) * (k - 2) / 2;
}
```