Segment Tree with Lazy Propagation

void update(int node, int start, int end, int l, int r, long delta) {
  push(node, start, end);
  if (r < start || end < l) return;
  if (l <= start && end <= r) {
    tree[node] += delta * (end - start + 1);
    lazy[node] += delta;
    return;
  }
  int mid = (start + end) / 2;
  update(2*node, start, mid, l, r, delta);
  update(2*node+1, mid+1, end, l, r, delta);
  tree[node] = tree[2*node] + tree[2*node+1];
}

void push(int node, int start, int end) {
  if (lazy[node] == 0 || start == end) return;
  int mid = (start + end) / 2;
  tree[2*node] += lazy[node] * (mid - start + 1);
  lazy[2*node] += lazy[node];
  tree[2*node+1] += lazy[node] * (end - mid);
  lazy[2*node+1] += lazy[node];
  lazy[node] = 0;
}