2395 Find Subarrays With Equal Sum

Given a 0-indexed integer array nums, determine whether there exist two subarrays of length 2 with equal sum. Note that the two subarrays must begin at different indices.

Return true if these subarrays exist, and false otherwise.

A subarray is a contiguous non-empty sequence of elements within an array.

Example 1:

Input: nums = [4,2,4]
Output: true
Explanation: The subarrays with elements [4,2] and [2,4] have the same sum of 6.

Example 2:

Input: nums = [1,2,3,4,5]
Output: false
Explanation: No two subarrays of size 2 have the same sum.

Example 3:

Input: nums = [0,0,0]
Output: true
Explanation: The subarrays [nums[0],nums[1]] and [nums[1],nums[2]] have the same sum of 0. 
Note that even though the subarrays have the same content, the two subarrays are considered different because they are in different positions in the original array.

Constraints:

• 2 <= nums.length <= 1000

• -109 <= nums[i] <= 109

这题主要是1477 Find Two Non-overlapping Sub-arrays Each With Target Sum原题做不通，然后点开相关题目过来看看有啥灵感才做的。这里因为规定了长度为2，而且subarray可以overlap。所以直接loop一圈，两两算一个和，用set查重。找到了就return。T:O(n), S:O(n)

public boolean findSubarrays(int[] nums) {
    if (nums == null || nums.length == 0) {
        return false;
    }

    // <sum>
    Set<Integer> set = new HashSet<>();
    for (int i = 0; i < nums.length - 1; i++) {
        int sum = nums[i] + nums[i + 1];
        if (set.contains(sum)) {
            return true;
        }
        set.add(sum);
    }

    return false;
}