Max segment tree in c++

seg.cpp

class seg_tree {
  public:
    vector<int> arr;
    vector<int> tree;
    int n;
  seg_tree(vector<int> x) {
    n = x.size();
    arr = x;
    tree.resize(4*n);
    build(0, 0, arr.size()-1);
  }
 
  int build(int node, int l, int r) {
    if(l>r)
      return 0;
 
    if(l==r) {
      tree[node] = arr[l];
      return tree[node];
    }
 
    int mid = (l+r)/2;
    int left = build(2*node+1, l, mid);
    int right = build(2*node+2, mid+1, r);
    tree[node] = max(left, right);
    return tree[node];
  }
 
  int query(int node, int x, int y, int l, int r) {
    if(l>y or r<x or l>r)
      return -inf;
 
    if(l<=x and y<=r)
      return tree[node];
 
    int mid = (x+y)/2;
    return max(query(2*node+1, x, mid, l, r), query(2*node+2, mid+1, y, l, r));
  }
 
  int q(int l, int r) {
    return query(0, 0, arr.size()-1, l, r);
  }
};