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Author: assassint2017

Longest Consecutive Sequence/Longest_Consecutive_Sequence.cpp

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+// 题目要求是on的时间复杂度，首先使用nlgn的排序思想解决问题
+
+// Runtime: 12 ms, faster than 99.79% of C++ online submissions for Longest Consecutive Sequence.
+// Memory Usage: 9 MB, less than 98.36% of C++ online submissions for Longest Consecutive Sequence.
+
+class Solution 
+{
+public:
+    int longestConsecutive(vector<int>& nums) 
+    {
+        if (nums.size() == 0)    
+            return 0;
+        
+        sort(nums.begin(), hashmap.end());
+        
+        int maxLength = 1;
+        for (int i = 1, length = 1; i < nums.size(); i++)
+        {
+            if (num == nums[i - 1] + 1)
+            {
+                length++;
+                maxLength = max(maxLength, length);
+            }
+            else if (num == nums[i - 1])
+                ;
+            else
+                length = 1;
+        }
+        return maxLength;
+    }
+};
+
+// 思路二，on的时间复杂度的版本
+// Runtime: 16 ms, faster than 71.73% of C++ online submissions for Longest Consecutive Sequence.
+// Memory Usage: 10.2 MB, less than 37.71% of C++ online submissions for Longest Consecutive Sequence.
+class Solution 
+{
+public:
+    int longestConsecutive(vector<int>& nums) 
+    {
+        unordered_map<int, int> hashmap;
+        int maxLength = 0;
+
+        // 对数组中的每一个数字进行O(1)的计算
+        for (auto num : nums)
+        {
+            // 如果当前数字已经存在于哈希表中，就没有必要二次操作了
+            if (hashmap.find(num) == hashmap.end())
+            {
+                auto rightIter = hashmap.find(num + 1);
+                auto leftIter = hashmap.find(num - 1);
+
+                int left = leftIter == hashmap.end() ? 0 : leftIter->second;
+                int right = rightIter ==  hashmap.end() ? 0 : rightIter->second;
+
+                int length = left + right + 1;
+                maxLength = max(maxLength, length);
+
+                hashmap.insert(make_pair(num, length));
+                
+                hashmap.at(num - left) = length;
+                hashmap.at(num + right) = length;
+            }
+        }
+        return maxLength;
+    }
+};

Longest Consecutive Sequence/Longest_Consecutive_Sequence.py

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+# 思路一的py代码
+
+# Runtime: 40 ms, faster than 88.35% of Python3 online submissions for Longest Consecutive Sequence.
+# Memory Usage: 12.9 MB, less than 99.52% of Python3 online submissions for Longest Consecutive Sequence.
+
+class Solution:
+    def longestConsecutive(self, nums: 'List[int]') -> 'int':
+        if not nums:
+            return 0
+        
+        nums.sort()
+        
+        Length, maxLength = 1, 1
+        for i in range(1, len(nums)):
+            if nums[i] == nums[i - 1] + 1:
+                Length += 1
+                maxLength = max(maxLength, Length)
+            elif nums[i] == nums[i - 1]:
+                pass
+            else:
+                Length = 1
+        
+        return maxLength
+
+# 思路二的py代码
+# Runtime: 40 ms, faster than 88.35% of Python3 online submissions for Longest Consecutive Sequence.
+# Memory Usage: 13.4 MB, less than 66.67% of Python3 online submissions for Longest Consecutive Sequence.
+
+class Solution:
+    def longestConsecutive(self, nums: 'List[int]') -> 'int':
+        hashmap = dict()
+        maxLength = 0
+
+        for num in nums:
+            if num not in hashmap:
+
+                right = hashmap[num + 1] if num + 1 in hashmap else 0
+                left = hashmap[num - 1] if num - 1 in hashmap else 0
+
+                length = left + right + 1
+                maxLength = max(length, maxLength)
+
+                hashmap[num] = length
+                hashmap[num - left] = length
+                hashmap[num + right] = length
+        
+        return maxLength
+