CodePudding user response:

This is not a O (N) is ok?

 int main () {
Int I, n, sum=0, FLG=1; 
The scanf (" % d ", & amp; N); 
For (I=1; I<=n; I++) {
The sum +=FLG * I; 
FLG *=1; 
} 
Printf (" % d \ n ", sum); 
return 0; 
} 

CodePudding user response:

Obviously every two to 1, until N is N/2 time complexity O (1)

CodePudding user response:

Of course, if you use the formula directly, O (1) can

 int main () {
Int I, n, sum=0, FLG=1; 
The scanf (" % d ", & amp; N); 
Sum=(1) * (n/2) + (n % 2==0? 0, n);//by skills, each is the sum of the two - 1, whether n is even, if it is an even number is 1 * n/2, otherwise again + n 
Printf (" % d \ n ", sum); 
return 0; 
} 

CodePudding user response:

The O (1) direct formula
1-2=1;
3-4=1;
,,,,,,

If N is an even number is equal to 1 * N/2
An odd number N + (N/2) * (1)

CodePudding user response:

Direct general term formula results
Time complexity O (1)
finished