arithmetic_slices_ii_subsequence.go

package problem0446

/*
Given an integer array nums, return the number of all the arithmetic subsequences of nums.
A sequence of numbers 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.
For example, [1, 1, 2, 5, 7] is not an arithmetic sequence.
A subsequence of an array is a sequence that can be formed by removing some elements (possibly none) of the array.
For example, [2,5,10] is a subsequence of [1,2,1,2,4,1,5,10].
The test cases are generated so that the answer fits in 32-bit integer.
*/

func numberOfArithmeticSlices(nums []int) int {
	var res, diff, c1, c2 int
	var cache = make([]map[int]int, len(nums))
	for i := range nums {
		cache[i] = map[int]int{}
		for j := 0; j < i; j++ {
			diff = nums[i] - nums[j]
			c1 = cache[i][diff]
			c2 = cache[j][diff]
			res += c2
			cache[i][diff] = c1 + c2 + 1
		}
	}
	return res
}