solve : #240 (Longest Consecutive Sequence) with Java

Author: kdh-92

longest-consecutive-sequence/kdh-92.java

@@ -0,0 +1,61 @@
+/**
+ * Constraints:
+ * - 0 <= nums.length <= 105
+ * - -109 <= nums[i] <= 109
+ *
+ * Output
+ * - 가장 긴 길이
+ *
+ * 풀이 특이점
+ * - 둘다 시간복잡도는 O(N)으로 생각되는데 Runtime의 결과 차이가 꽤 크게 나온 점
+ */
+
+class Solution {
+    public int longestConsecutive(int[] nums) {
+        // (1) Set & num -1
+        // 시간복잡도 : O(N)
+        // Runtime : 1267ms Beats 5.15%
+        // Memory : 63.30MB Beats 62.58%
+        // Set<Integer> uniqueNums = Arrays.stream(nums).boxed().collect(Collectors.toSet());
+        // int result = 0;
+
+        // for (int num : nums) {
+        //     if (uniqueNums.contains(num - 1)) continue;
+        //     int length = 1;
+        //     while (uniqueNums.contains(num + length)) length += 1;
+        //     result = Math.max(length, result);
+        // }
+
+        // return result;
+
+        // (2) HashMap
+        // 시간복잡도 : O(N)
+        // Runtime : 38ms Beats 46.54%
+        // Memory : 66.45MB Beats 51.28%
+        HashMap<Integer, Boolean> hm = new HashMap<>();
+
+        for(int i=0; i<nums.length; i++){
+            hm.put(nums[i], false);
+        }
+
+        for(int key : hm.keySet()){
+            if(hm.containsKey(key - 1)== false){
+                hm.put(key, true);
+            }
+        }
+
+        int max = 0;
+        for(int key : hm.keySet()){
+            int k =1;
+            if(hm.get(key) == true){
+                while(hm.containsKey(key + k) == true){
+                    k++;
+                }
+            }
+
+            max = Math.max(max, k);
+        }
+
+        return max;
+    }
+}