(Java) Leetcode 413. Arithmetic slices--arithmetic progression Division

A sequence of number is called arithmetic if it consists of in least three elements and if the difference between any Consecutive elements is the same.

For example, these is arithmetic sequence:

1, 3, 5, 7, 97, 7, 7, 73,-1,-5, 9

The following sequence is not arithmetic.

1, 1, 2, 5, 7

A zero-indexed array a consisting of N numbers is given. A slice of that array was any pair of integers (p, Q) such that 0 <= P < Q < N.

A Slice (P, Q) of array A is called arithmetic if the sequence:
A[p], A[p + 1], ..., a[q-1], a[q] is arithmetic. In particular, this means that P + 1 < Q.

The function should return the number of arithmetic slices in the array A.

Example:

A = [1, 2, 3, 4]return:3, for 3 arithmetic slices in A: [1, 2, 3], [2, 3, 4] and [1, 2, 3, 4] itself.

Thought for a long while this problem unexpectedly is a law problem ... Sometimes it's hard to fathom what problems need to be deduced and what the problem is to find the law.

The result is 1 if the array is {A-n-a};

If the array is {1,2,3,4}, the result is 3;

If the array is {1,2,3,4,5}, the result is 6;

If the array is {1,2,3,4,5,6}, the result is 10 ...

That is, if the newly-scanned element still retains a arithmetic progression relationship with the previous element, the number of newly formed sub-arithmetic progression will follow 1,2,3,4 ... The law increases. In fact, find the law of the problem to be made. So the point is to find the end of the difference sub-series, and at this time the result of the incremental update of the final result. When the arithmetic progression is not satisfied, the increment is reset to 1. See code below.

Java

classSolution { Public intNumberofarithmeticslices (int[] A) {if(A = =NULL|| A.length <= 2)return0; intCur = 1, res = 0, diff = a[1]-a[0];  for(inti = 2; i < a.length; i++) {            if(A[i]-a[i-1] = = diff) Res + = cur++; Else{diff= A[i]-a[i-1]; Cur= 1; }        }        returnRes; }   }

(Java) Leetcode 413. Arithmetic slices--arithmetic progression Division