# Can we use sort() to solve this question?

• If I use sort(), can I say my algorithm is O(n) ?
Thanks.

``````    bool compareVec( const int& a, const int& b) {
return a < b;
}
int longestConsecutive(vector<int> &num) {
int size = num.size();
if( size < 2 )
return size;
sort( num.begin(), num.end(), compareVec );
int len = 1;
int flag = 1;
for( int i = 1; i < size; ++i ) {
if( num[i] - num[i-1] == 1 ) {
flag++;
} else {
if( flag > len ) {
len = flag;
}
flag = 1;
}
}
if( flag > len ) {
len = flag;
}
return len;
}``````

• Using `sort()` will never be O(N), since it takes O(N log N).

When calculating time complexity, do not leave library function out.

• I just don't see why you define the function compareVec(), regarding that the elements contained in the vector are of type int. sort() will naturally use operator < to sort out the vector, won't it?
Besides, I also have some doubts about 'const int & a'. I agree with const, but I don't think it bothers using reference for an int.
As for sort, I tried it, and leetcode let it pass the test. However, as mentioned by shangrila, it does absolutely not satisfy the requirement.

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