Left part of segment + Right part of segment = Whole segment code example
Example 1: segment tree
// General Segment Tree struct
// Original source: https://codeforces.com/blog/entry/18051
template struct SegTree {
int size;
T defVal;
vector tree;
T (*op)(T, T);
SegTree (int size, T defVal, T (*op)(T, T))
: size(size), defVal(defVal), tree(vector(2*size)), op(op) {}
SegTree (vector v, T defVal, T (*op)(T, T))
: SegTree(v.size()/2, defVal, op) {
for (int i = 0; i0; --i) {
tree[i] = op(tree[i<<1], tree[i<<1|1]);
}
}
T query (int l, int r) {
l += size, r += size+1;
T res;
for (res = defVal; l>= 1, r >>= 1) {
if (l&1) res = op(res, tree[l++]);
if (r&1) res = op(res, tree[--r]);
}
return res;
}
void update (int i, T val) {
i += size;
for (tree[i] = val; i>1; i >>= 1) {
tree[i>>1] = op(tree[i], tree[i^1]);
}
}
};
Example 2: Segment tree
void build(int node, int start, int end)
{
if(start == end)
{
// Leaf node will have a single element
tree[node] = A[start];
}
else
{
int mid = (start + end) / 2;
// Recurse on the left child
build(2*node, start, mid);
// Recurse on the right child
build(2*node+1, mid+1, end);
// Internal node will have the sum of both of its children
tree[node] = tree[2*node] + tree[2*node+1];
}
}