LongestConsecutiveSequence

Change-Id: I969193b628c0b892905721fe32abacbdf5a71481

Author: applewjg

LongestConsecutiveSequence.java

@@ -0,0 +1,43 @@
+/*
+ Author:     Andy, nkuwjg@gmail.com
+ Date:       Jun 18, 2014
+ Problem:    Longest Consecutive Sequence
+ Difficulty: Hard
+ Source:     https://oj.leetcode.com/problems/longest-consecutive-sequence/
+ Notes:
+ Given an unsorted array of integers, find the length of the longest consecutive 
+ elements sequence.
+ For example,
+ Given [100, 4, 200, 1, 3, 2],
+ The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.
+ Your algorithm should run in O(n) complexity.
+
+ Solution 1: Update solution. 
+*/
+
+public class Solution {
+    public int longestConsecutive(int[] num) {
+        int size = num.length;
+        HashMap<Integer, Integer> unmap = new HashMap<Integer, Integer>();
+        int res = 0;
+        for (int i = 0; i < size; ++i) {
+            if (unmap.containsKey(num[i]) == true) continue;
+            int val = num[i];
+            if (unmap.containsKey(val - 1) == true && unmap.containsKey(val + 1) == true) {
+                unmap.put(val, unmap.get(val - 1) + unmap.get(val + 1) + 1);
+                unmap.put(val - unmap.get(val - 1), unmap.get(val));
+                unmap.put(val + unmap.get(val + 1), unmap.get(val));
+            } else if (unmap.containsKey(val - 1) == true) {
+                unmap.put(val, unmap.get(val - 1) + 1);
+                unmap.put(val - unmap.get(val - 1), unmap.get(val));
+            } else if (unmap.containsKey(val + 1) == true) {
+                unmap.put(val, unmap.get(val + 1) + 1);
+                unmap.put(val + unmap.get(val + 1), unmap.get(val));   
+            } else {
+                unmap.put(val, 1);
+            }
+            res = Math.max(res, unmap.get(val));
+        }
+        return res;
+    }
+}