LeetCode-in-Java

1630. Arithmetic Subarrays

Medium

A sequence of numbers is called arithmetic if it consists of at least two elements, and the difference between every two consecutive elements is the same. More formally, a sequence s is arithmetic if and only if s[i+1] - s[i] == s[1] - s[0] for all valid i.

For example, these are arithmetic sequences:

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

The following sequence is not arithmetic:

1, 1, 2, 5, 7

You are given an array of n integers, nums, and two arrays of m integers each, l and r, representing the m range queries, where the ith query is the range [l[i], r[i]]. All the arrays are 0-indexed.

Return a list of boolean elements answer, where answer[i] is true if the subarray nums[l[i]], nums[l[i]+1], ... , nums[r[i]] can be rearranged to form an arithmetic sequence, and false otherwise.

Example 1:

Input: nums = [4,6,5,9,3,7], l = [0,0,2], r = [2,3,5]

Output: [true,false,true]

Explanation:

In the 0^th query, the subarray is [4,6,5].

This can be rearranged as [6,5,4], which is an arithmetic sequence.

In the 1^st query, the subarray is [4,6,5,9]. This cannot be rearranged as an arithmetic sequence.

In the 2^nd query, the subarray is [5,9,3,7]. This can be rearranged as [3,5,7,9], which is an arithmetic sequence.

Example 2:

Input: nums = [-12,-9,-3,-12,-6,15,20,-25,-20,-15,-10], l = [0,1,6,4,8,7], r = [4,4,9,7,9,10]

Output: [false,true,false,false,true,true]

Constraints:

• n == nums.length
• m == l.length
• m == r.length
• 2 <= n <= 500
• 1 <= m <= 500
• 0 <= l[i] < r[i] < n
• -105 <= nums[i] <= 105

Solution

import java.util.ArrayList;
import java.util.List;

public class Solution {
    public List<Boolean> checkArithmeticSubarrays(int[] nums, int[] l, int[] r) {
        List<Boolean> result = new ArrayList<>();
        int n = l.length;
        for (int i = 0; i < n; i++) {
            result.add(check(nums, l[i], r[i]));
        }
        return result;
    }

    private boolean check(int[] nums, int l, int r) {
        int n = r - l;
        if (n == 0) {
            return true;
        }
        int max = Integer.MIN_VALUE;
        int min = Integer.MAX_VALUE;
        for (int i = l; i <= r; i++) {
            max = Math.max(max, nums[i]);
            min = Math.min(min, nums[i]);
        }
        if ((max - min) % n != 0) {
            return false;
        }
        int diff = (max - min) / n;
        if (diff == 0) {
            return true;
        }
        boolean[] checked = new boolean[max - min + 1];
        for (int i = l; i <= r; i++) {
            int currentDiff = nums[i] - min;
            if (checked[currentDiff] || currentDiff % diff != 0) {
                return false;
            }
            checked[currentDiff] = true;
        }
        return true;
    }
}

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