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.
1
2
3
4
5
6
7
8
9
10
| 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
Solution Brute Force#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
| class Solution {
public int numberOfArithmeticSlices2(int[] nums) {
if (nums.length < 3) {
return 0;
}
int count = 0;
for (int i = 0; i < nums.length - 2; i++) {
int delta = nums[i] - nums[i+1] ;
if (delta == nums[i + 1] - nums[i+2]) {
count++;
int j = i + 2;
while (j + 1 < nums.length && delta == nums[j] - nums[j+1]) {
count++;
j++;
}
}
}
return count;
}
}
|
Solution DP#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
| class Solution {
/*
123456
123456
112345
123 1234 12345 123456
234 2345 23456
345 3456
456
*/
public int numberOfArithmeticSlices(int[] nums) {
int[] dp = new int[nums.length];
int sum = 0;
for (int i = 2; i < nums.length; i++) {
if (nums[i] - nums[i - 1] == nums[i - 1] - nums[i - 2]) {
dp[i] = dp[i - 1] + 1;
sum += dp[i];
}
}
return sum;
}
}
|