Updating the segment tree

Updating the segment tree.cpp

// We want to update the value associated with index in the input array 
void update(int index, T value) {
  update(1, 0, N-1, index, value);
}

// nodes[stIndex] is responsible for segment [lo, hi]
void update(int stIndex, int lo, int hi, int index, T value) {
  if (lo == hi) {
    nodes[stIndex].assignLeaf(value);
    return;
  }
  
  int left = 2 * stIndex, right = left + 1, mid = (lo + hi) / 2;
  if (index <= mid)
    update(left, lo, mid, index, value);
  else
    update(right, mid+1, hi, index, value);
  
  nodes[stIndex].merge(nodes[left], nodes[right]);
}