algorithm/segment_tree.cpp at main · ihbadhon/algorithm · GitHub

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vi v, tree;

void buildTree(int node, int l, int r)
{
    if(l==r)
    {
        tree[node] = v[l];
        return;
    }
    int l_node = node*2;
    int r_node = node* 2 + 1;
    int mid = l+ (r-l)/2;
    buildTree(l_node,l, mid);
    buildTree(r_node, mid+1, r);
    tree[node] = tree[l_node] + tree[r_node];
}

int query(int node, int l, int r, int i , int j)
{
    if(i>r or j<l)
    return 0;
    if(i<=l and j>=r)
    return tree[node];

    int l_node = node*2;
    int r_node = node*2 + 1;
    int mid = l + (r-l)/2;
    int sum1 = query(l_node, l, mid, i, j);
    int sum2 = query(r_node, mid+1, r, i, j);
    return sum1 + sum2;
}

void update(int node, int l, int r, int i, int val)
{
    if(i<l or i>r)
    return;
    if(l==r)
    {
        tree[node] = val;
        return;
    }
    int l_node = node*2;
    int r_node = node*2+1;
    int mid = l+ (r-l)/2;
    update(l_node,l, mid, i, val);
    update(r_node, mid+1, r, i, val);
    tree[node] = tree[l_node] + tree[r_node];

}