ArithmeticSlices413.kt

package medium

/**
 * An integer array is called arithmetic if it consists of at least three elements and if the difference between any two consecutive elements is the same.

For example, [1,3,5,7,9], [7,7,7,7], and [3,-1,-5,-9] are arithmetic sequences.
Given an integer array nums, return the number of arithmetic subarrays of nums.

A subarray is a contiguous subsequence of the array.



Example 1:

Input: nums = [1,2,3,4]
Output: 3
Explanation: We have 3 arithmetic slices in nums: [1, 2, 3], [2, 3, 4] and [1,2,3,4] itself.
Example 2:

Input: nums = [1]
Output: 0


Constraints:

1 <= nums.length <= 5000
-1000 <= nums[i] <= 1000
 */
fun numberOfArithmeticSlices(nums: IntArray): Int {
    if (nums.size < 3) return 0

    var total = 0
    val dp = IntArray(nums.size)
    dp[0] = 0
    dp[1] = 0
    for (i in 2 until nums.size) {
        val diff1 = nums[i] - nums[i - 1]
        val diff2 = nums[i - 1] - nums[i - 2]
        if (diff1 == diff2) {
            dp[i] = dp[i - 1] + 1
            total += dp[i]
        } else
            dp[i] = 0
    }
    return total
}