### nikizakr's blog

By nikizakr, history, 4 months ago, ,

the build function in segment tree :

void build(int id = 1,int l = 0,int r = n){
if(r - l < 2){	//	l + 1 == r
s[id] = a[l];
return ;
}
int mid = (l+r)/2;
build(id * 2, l, mid);
build(id * 2 + 1, mid, r);
s[id] = s[id * 2] + s[id * 2 + 1];
}


divide and conquer algorithm to find maximum element in array :

int Max(int s = 1 , int e = n){
if(s == e) return arr[s] ;
int choice1 = arr[s] , choice2 = arr[e] ;
choice1 = max( choice1 , Max( s , (s + e)/2 ) ;
choice2 = max( choice2 , Max( (s + e)/2 + 1 , e )   ;
return max(choice1 , choice2)  ;
}


why the complexity of the first function is O( n * log(n) ) And the second is O(n) thanks for your help :D

 » 4 months ago, # |   0 Auto comment: topic has been updated by nikizakr (previous revision, new revision, compare).
 » 4 months ago, # |   +11 The complexity of the first algorithm is also O(n).