find the largest subset of consecutive integers 找到最大的连续整数子集

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本文介绍了一种在包含重复元素的整数数组中找出最长连续整数序列的方法。通过使用哈希映射来存储每个元素及其连续序列，可以在O(n)时间内高效地解决问题。

Find the largest subset of consecutive integers 找到最大的连续整数子集

Given an int array which might contain duplicates, find the largest subset of it which form a sequence.
Eg. {1,6,10,4,7,9,5}
then ans is 4,5,6,7

一个简单的解法是：

Sort the array
Find the longest subset
Remove duplicate numbers

但是， Can this be done in O(n) time ?

Approach:
A = {1,6,10,4,7,9,5}

For each number A[i], put A[i] in hashMap<Int, List>
Also check if (A[i]+1) and (A[i]-1) exists in the Map,
If hashMap.contains((A[i]+1)) is true then append A[i] to the hashMap.get((A[i]+1));
If hashMap.contains((A[i]-1)) is true then append A[i] to the hashMap.get((A[i]-1));
And Append hashMap.get(A[i]+1) and hashMap.get(A[i]-1) to hashMap.get(A[i]);

In the end the iterate through all the keys of the hashMap and the largest List of hashMap.get(A[i]) is the longest sequence that exists in the input array.

Input Array for the below code:
A = {2, 3, 9, 10, 11, 4, 13, 5, 15, 6, 17, 7};
Output:

subset which forms the longest consecutive sequence:
2 3 4 5 6 7