[LeetCode][P128]Longest Consecutive Sequence

Author: sgirabin

leetcode/src/algorithms/Solution.java

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+class Solution {
+    
+    public int longestConsecutive(int[] nums) {
+        
+        Set<Integer> num_set = new HashSet<Integer>();
+        for (int num : nums) {
+            num_set.add(num);
+        }
+
+        int longestStreak = 0;
+
+        for (int num : num_set) {
+            if (!num_set.contains(num-1)) {
+                int currentNum = num;
+                int currentStreak = 1;
+
+                while (num_set.contains(currentNum+1)) {
+                    currentNum += 1;
+                    currentStreak += 1;
+                }
+
+                longestStreak = Math.max(longestStreak, currentStreak);
+            }
+        }
+
+        return longestStreak;
+    }
+    
+}

leetcode/src/algorithms/readme.md

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+128. Longest Consecutive Sequence
+
+Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.
+
+You must write an algorithm that runs in O(n) time.
+
+ 
+
+Example 1:
+
+Input: nums = [100,4,200,1,3,2]
+Output: 4
+Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.
+Example 2:
+
+Input: nums = [0,3,7,2,5,8,4,6,0,1]
+Output: 9
+ 
+
+Constraints:
+
+0 <= nums.length <= 105
+-109 <= nums[i] <= 109