add solution of longest-consecutive-sequence

Author: jinhyungrhee

longest-consecutive-sequence/jinhyungrhee.java

@@ -0,0 +1,40 @@
+import java.util.*;
+
+class Solution {
+    public int longestConsecutive(int[] nums) {
+        Set<Integer> table = new HashSet<>();
+        int longest = 0;
+
+        for(int n : nums) {
+            table.add(n);
+        }
+
+        // O(N)
+        for (int num : table) {
+            if (!table.contains(num - 1)) {
+                int currentNum = num;
+                int currentStreak = 1;
+
+                while (table.contains(currentNum + 1)) {
+                    currentNum++;
+                    currentStreak++;
+                }
+                longest = Math.max(longest, currentStreak);
+            }
+        }
+
+        /** TIME OUT 발생!
+         *
+        for (int n : nums) {
+            if (table.contains(n - 1)) continue;
+            int len = 1;
+            while (table.contains(n + len)){
+                len++;
+            }
+            longest = Math.max(len, longest);
+        }
+         */
+
+        return longest;
+    }
+}