413. Arithmetic Slices

Problem

Tags: Array, Dynamic Programming

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

Code

C

// 413. Arithmetic Slices (10/1/54138)
// Runtime: 3 ms (39.58%) Memory: 6.15 MB (0.00%) 

int numberOfArithmeticSlices (int nums[], int size) {
    int count = 0, curr = 2;
    
    for (int i = 2; i < size; i++) {
        if (nums[i] - nums[i - 1] == nums[i - 1] - nums[i - 2]) {
            curr++;
            count += curr > 2 ? curr - 2 : 0;
        } else {
            curr = 2;
        }
    }
    
    return count;
}