LeetCode_Longest Consecutive Sequence
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.
The key point is that for each number say Val in the array, we only need to determine whether its neighbor (Val-1 and Val+1) is in the array and for a consecutive sequence we only need to know the the boundary and the length information。
class Solution {
public:
int longestConsecutive(vector<int> &num) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
int size = num.size();
if(size < ) return size; map<int, int> myMap;
for(int i = ; i< num.size(); i++)
myMap.insert(pair<int, int>(num[i],)); int maxLen = ;
map<int, int>::iterator m_it;
map<int, int>::iterator temp_it; for(m_it = myMap.begin(); m_it != myMap.end();m_it++)
{ if(m_it->second == ) continue;
int len = ;
int low = m_it->first;
int high = low;
while(true)
{
temp_it= myMap.find(low-);
if(temp_it == myMap.end())
break;
low--;
len++;
temp_it->second = ;
} while(true)
{
temp_it= myMap.find(high+) ;
if(temp_it == myMap.end())
break;
high++;
len++ ;
temp_it->second = ;
} maxLen = maxLen < len ? len : maxLen ; } return maxLen ; }
};
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