# Plain Vanilla java DP solution: probably easier to understand than others

• This solution has the benefit that it can be easily extended to calculate all possible arithmetic slides (not necessarily one by one close to each others), for example:

Given array [1,2,3,4,5], if "[1,3,5]" is also counted, the following code can be adapted to accommodate that by looping through 'secondIndex'

``````public class Solution {
public int numberOfArithmeticSlices(int[] A) {
// algorithm: dynamic programming; assume we have the results for the previous (n-1) numbers
//  now with the new number, check how many new arithmetic slices ended with the last number
if (null == A || 2 >= A.length) {
return 0;
}
int[] results = new int[A.length];
// this array records the number of arithmetic slice ENDED WITH IT
results[0] = 0;
results[1] = 0;
for (int firstIndex = 0; firstIndex < A.length - 2; firstIndex++) {
int firstNum = A[firstIndex];
int secondIndex = firstIndex + 1;

int secondNum = A[secondIndex];
// check arithmetic sequence
int numDelta = secondNum - firstNum;

int nextIndex = secondIndex + 1;
int nextNum = secondNum + numDelta;
while (nextIndex < A.length) {
// find an arithmetic sequence
if (A[nextIndex] == nextNum) {
results[nextIndex] ++;
} else {
// make sure we break here -- do NOT check subsequent numbers!
break;
}
// proceed
nextIndex ++;
nextNum += numDelta;
}
}

// now count the total number of arithmetic slices
int count = 0;
for (int index = 0; index < A.length; index++) {
count += results[index];
}
return count;
}
}``````

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