Longest Consecutive Sequence

https://leetcode.com/problems/longest-consecutive-sequence/description/

HashMap

https://discuss.leetcode.com/topic/6148/my-really-simple-java-o-n-solution-accepted

public class Solution {
    public int longestConsecutive(int[] nums) {
        int max = 0;
        if(nums == null || nums.length == 0){
            return max;
        }

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

        for(Integer e : nums){
            if(!map.containsKey(e)){
                int left = map.containsKey(e - 1)? map.get(e - 1) : 0;
                int right = map.containsKey(e + 1)? map.get(e + 1) : 0;
                int sum = 1 + left + right;
                map.put(e, sum);
                max = Math.max(max, sum);
                map.put(e - left, sum);
                map.put(e + right, sum);    
            }else{
                continue;
            }
        }

        return max;
    }
}
set.contains(value) return boolean value!!!


public int longestConsecutive(int[] nums) {
    if(nums == null || nums.length == 0) return 0;

    Set<Integer> set = new HashSet<Integer>();

    for(int num: nums) set.add(num);
    int max = 1;
    for(int num: nums) {
        if(set.remove(num)) {//num hasn't been visited
            int val = num;
            int sum = 1;
            while(set.remove(val-1)) val--;
            sum += num - val;

            val = num;
            while(set.remove(val+1)) val++;
            sum += val - num;

            max = Math.max(max, sum);
        }
    }
    return max;
}

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