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

http://blog.csdn.net/linhuanmars/article/details/22964467

public class Solution {
    public int longestConsecutive(int[] num) {
        
        // Solution A:
        // return longestConsecutive_Sort(num);
        
        // Solution B:
        return longestConsecutive_Graph(num);
    }

    ///////////////
    // Solution B: Graph
    //
    private int longestConsecutive_Graph(int[] n)
    {
        // 把这n个数 构建成一个 graph
        // 如果 两个数 相差 1， 他们相连 
        // 
        // 建立 一个set
        // 取 1 点 ， bfs 它， 更新max
        // bfs完成， 如果set 还有其他点 取下一点
        
        Set<Integer> set = new HashSet<>();
        for (int i : n)
            set.add(i);
            
        int max = 1;
        while (!set.isEmpty())
        {
            // Get a random point.
            int i = set.iterator().next();
            int curlen = 1;
            set.remove(i);
            
            // BFS it
            int j = i + 1;
            while (set.contains(j))
            {
                curlen ++;
                set.remove(j);
                j ++;
            }
            
            j = i - 1;
            while (set.contains(j))
            {
                curlen ++;
                set.remove(j);
                j --;
            }
            
            max = Math.max(max, curlen);
        }
        
        return max;
    }
    
    
    ///////////////
    // Solution A: Sort
    //
    private int longestConsecutive_Sort(int[] n)
    {
        Arrays.sort(n);
        int max = 1;
        int cur = 1;
        for (int i = 0 ; i < n.length - 1 ; i ++)
        {
            if (n[i + 1] - n[i] == 1)
            {
                cur ++;
                max = Math.max(max, cur);
            }
            else if (n[i + 1] == n[i])
            {
                continue;
            }
            else
            {
                cur = 1;
            }
        }
        return max;
    }
}

[LeetCode]128 Longest Consecutive Sequence