Create Longest_Consecutive_Sequence.js

Author: ignacio-chiazzo

LeetcodeProblems/Longest_Consecutive_Sequence.js

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+/*
+Longest Consecutive Sequence
+
+https://leetcode.com/problems/longest-consecutive-sequence/
+
+Given an unsorted array of integers, find the length of the longest consecutive elements sequence.
+
+Your algorithm should run in O(n) complexity.
+
+Example:
+
+Input: [100, 4, 200, 1, 3, 2]
+Output: 4
+Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.
+*/
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var longestConsecutive = function(nums) {
+  if(nums.length === 0) 
+    return 0;
+  var setNums = new Set();
+  for(var i = 0; i < nums.length; i++)
+    setNums.add(nums[i]);
+  
+  var cons = 1;
+  var currentCons = 1;
+  for(var i = 0; i < nums.length; i++) {
+    var number = nums[i];
+    if(setNums.has(number)) {
+      setNums.delete(number);
+      var prevNum = number - 1;
+      while(setNums.has(prevNum)){
+        currentCons++;
+        setNums.delete(prevNum);
+        prevNum--;
+      }
+      
+      var nextNum = number + 1;
+      while(setNums.has(nextNum)){
+        currentCons++;
+        setNums.delete(nextNum);
+        nextNum++;
+      }
+      
+      if(currentCons > cons)
+        cons = currentCons    
+    }
+    currentCons = 1;
+  }
+  return cons;
+};
+
+
+var main = function() {
+  console.log(longestConsecutive([100, 1, 200, 3, 2, 400, 201]));
+  console.log(longestConsecutive([1,2,3,4, 100, 1, 200, 3, 2, 400, 201]));
+  console.log(longestConsecutive([1, 400, 201, 403, 398]));
+  console.log(longestConsecutive([]));
+  console.log(longestConsecutive([2]));
+}
+
+module.exports.main