"Set all elements in to value " is different from "add to range."
For range set, the lazy value represents "set to this value," not "add this value." Use a sentinel (like or None) to indicate "no pending set."
def rangeSet(node, start, end, l, r, val):
if r < start or end < l:
return
if l <= start and end <= r:
tree[node] = val * (end - start + 1)
lazy[node] = val
return
pushDown(node, start, end)
mid = (start + end) // 2
rangeSet(2*node, start, mid, l, r, val)
rangeSet(2*node+1, mid+1, end, l, r, val)
tree[node] = tree[2*node] + tree[2*node+1]
The push down for "set" overwrites children's values and lazy, rather than adding to them.