Arithmetic Slices LeetCode

A sequence of number 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, these are arithmetic sequence:

• 1, 3, 5, 7, 9
• 7, 7, 7, 7
• 3, -1, -5, -9

The following sequence is not arithmetic.

• 1, 1, 2, 5, 7

A zero-indexed array A consisting of N numbers is given. A slice of that array is any pair of integers (P, Q) such that 0 <= P < Q < N.

A slice (P, Q) of array A is called arithmetic if the sequence:

A[P], A[p + 1], ..., A[Q - 1], A[Q] is arithmetic. In particular, this means that P + 1 < Q.

The function should return the number of arithmetic slices in the array A.

Example:

• Input A = [1, 2, 3, 4]
• Output = 3, for 3 arithmetic slices in A: [1, 2, 3], [2, 3, 4] and [1, 2, 3, 4] itself.

This is an interesting interview problem and is popular in LeetCode A collection of hundreds of interview questions and solutions are available in our blog at Interview Question

Solution

	/**
	A sequence of number 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, these are arithmetic sequence:
	1, 3, 5, 7, 9
	7, 7, 7, 7
	3, -1, -5, -9
	The following sequence is not arithmetic.
	1, 1, 2, 5, 7
	A zero-indexed array A consisting of N numbers is given. A slice of that array is any pair of integers (P, Q) such that 0 <= P < Q < N.
	A slice (P, Q) of array A is called arithmetic if the sequence:
	A[P], A[p + 1], ..., A[Q - 1], A[Q] is arithmetic. In particular, this means that P + 1 < Q.
	The function should return the number of arithmetic slices in the array A.
	Example:
	A = [1, 2, 3, 4]
	return: 3, for 3 arithmetic slices in A: [1, 2, 3], [2, 3, 4] and [1, 2, 3, 4] itself.
	*/
	public class ArithmeticSlices{
	public static int numberOfArithmeticSlices(int[] nums) {
	int cur=0;
	int count = 0;
	for(int i =2;i<nums.length; i++){
	if(nums[i]-nums[i-1] == nums[i-1]-nums[i-2]){
	//"curr" the number of different "Arithmetic Slices" ends at index = i
	curr++;
	count+=curr;
	}else{
	//start newsubarray because the slice property is violated here
	curr = 0;
	}
	}
	return count;
	}
	public static void main(String args[]){
	int[] nums = new int[]{1, 2, 3, 4};
	System.out.println(numberOfArithmeticSlices(nums));
	nums = new int[]{7, 7, 7, 7, 7};
	System.out.println(numberOfArithmeticSlices(nums));
	nums = new int[]{1, 1, 2, 5, 7};
	System.out.println(numberOfArithmeticSlices(nums));
	}
	}

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