solve longest consecutive sequence

Author: samcho0608

longest-consecutive-sequence/samcho0608.java

@@ -0,0 +1,33 @@
+import java.util.HashSet;
+import java.util.Set;
+
+class Solution {
+    // * nums is unsorted
+    // * return: length of longest consecutive elements sequence
+    // * req: O(N) time
+    public int longestConsecutive(int[] nums) {
+        Set<Integer> uniq = new HashSet<>();
+
+        // O(N)
+        for(int num : nums) {
+            uniq.add(num);
+        }
+
+        // O(N)
+        int maxLen = 0;
+        for(int num : uniq) {
+            // 기존에 시작된 consecutive sequence가 있으면 스킵
+            if(uniq.contains(num - 1)) continue;
+
+            // count till end of consecutive sequence
+            int len = 1;
+            for(int i = 1; uniq.contains(num + i); i++) {
+                len++;
+            }
+
+            maxLen = Math.max(maxLen, len);
+        }
+
+        return maxLen;
+    }
+}