SegmentTree.cpp

//Implementation based off: http://codeforces.com/blog/entry/18051

const int MAXN = 1e5;  // limit for array size
int n;  // array size
int t[2 * MAXN]; // one-based tree structure

void build() {  // build the tree
  for (int i = n - 1; i > 0; --i)
  	t[i] = t[i<<1] + t[i<<1|1];
}

void modify(int p, int value) {  // set value at position p
  for (t[p += n] = value; p > 1; p >>= 1)
  	t[p>>1] = t[p] + t[p^1];
}

int query(int l, int r) { //find the (sum, min, max) over range [l, r)
  int res = 0;
  for (l += n, r += n; l < r; l >>= 1, r >>= 1) {
    if (l&1) res += t[l++];
    if (r&1) res += t[--r];
  }
  return res;
}

int main() {
  scanf("%d", &n); //& is the reference operator. In this case it tells the program to store
  //the next input from stdin to n's location in memory
  for (int i = 0; i < n; ++i)
  	scanf("%d", t + n + i); //store array values in the second half of tree array (represents
	//bottom of the tree)
  build();
  modify(0, 1);
  printf("%d\n", query(3, 11));
  return 0;
}