// Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

// For example,

// Given [100, 4, 200, 1, 3, 2],

// The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.

// Your algorithm should run in O(n) complexity.

public class Solution {

public int longestConsecutive(int[] nums) {

int res = 0;

HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();

for(int n : nums) {

if(!map.containsKey(n)) {

int left = (map.containsKey(n - 1)) ? map.get(n - 1) : 0;

int right = (map.containsKey(n + 1)) ? map.get(n + 1) : 0;

int sum = left + right + 1;

map.put(n, sum);

res = Math.max(res, sum);

map.put(n - left, sum);

map.put(n + right, sum);

}

else {

continue;

}

}

return res;

}

}