segment-tree | Rust implementation of two segment trees | Dataset library

Hint regarding the editorial (the details of which I am uncertain about): if we can solve the problem for all the intervals that include both A[i] and A[i+1], where i divides A in half, in O(n) time, then we can solve the whole problem in O(n log n) time using divide and conquer, solving left and right separately, and adding to that the intervals that overlap both left and right.

The variable p doesn't mean parent, it means child. In for loop, i is child node, and we update value of i's parent.

tree[p+n] = value;: update the value of leave node (node without children). Then we update value of node's parent from the leave node. tree[i>>1] = tree[i] + tree[i^1];, tree[i>>1] is tree[i]' parent.

For example: the array size is 16 (the tree size is 32) and I want to update arr[8]. So I call updateTreeNode(8, value). First three[8+16] is updated, which corresponds to arr[8]. Then p is set to 24. In for loop, we update p's parent (tree[12]), then set p to p/2 (p=12), until p doesn't have parent.

If l and r is even, we add the parent's value in next recurrence. That's the function of segment tree, to avoid querying each element in the interval.

For example: the array size is 16 and I want to query [8,10). In segment tree, the interval is [24,26). We don't need to add value of tree[24] and tree[25], we add value of tree[12]!