longest-consecutive-sequence solution

Author: ohgyulim

longest-consecutive-sequence/ohgyulim.java

@@ -0,0 +1,32 @@
+import java.util.*;
+
+class Solution {
+    /* 시간 복잡도: O(N)
+    * - for 루프: O(N) O(N)
+    *   - HashSet(add, contains): O(1)
+    * 
+    * 공간 복잡도: O(N), HashSet에 n개
+    */ 
+    public int longestConsecutive(int[] nums) {
+        Set<Integer> set = new HashSet<>();
+        for (int num : nums) {
+            set.add(num);
+        }
+
+        int answer = 0;
+        for (int num : set) {
+            if (!set.contains(num - 1)) {
+                int cur = num;
+                int count = 1;
+                while (set.contains(cur + 1)) {
+                    cur += 1;
+                    count += 1;
+                }
+                answer = Math.max(answer, count);
+            }
+        }
+
+        return answer;
+    }
+}
+