Practice-Coding/Maximum Sum In Subarray(Segment Tree) at master · PrakharRastogi123/Practice-Coding · GitHub

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#include<bits/stdc++.h>
using namespace std;
#define inf 0x3f3f
struct node{
  int sum,maxsum,bps,bss;
    node()
    {
        bps = bss = sum = -inf;
        maxsum= -inf;
    }
};
node merge(node l,node r){
    node mgd;
    mgd.maxsum=max(max(l.maxsum,r.maxsum),max(max((l.sum+r.bps),(r.sum+l.bss)),l.bss+r.bps));
    mgd.sum=l.sum+r.sum;
    mgd.bps=max(l.bps,l.sum+r.bps);
    mgd.bss=max(r.bss,r.sum+l.bss);
    return mgd;
}
node querry(int *arr,node *tree,int si,int ei,int ti,int l,int r){
    if(ei<l || si>r){
        node nullnode;
        return nullnode;
    }
    if(si>=l && ei<=r){
        return tree[ti];
    }
    int mid=(si+ei)/2;
    node lft=querry(arr,tree,si,mid,2*ti,l,r);
    node rgt=querry(arr,tree,mid+1,ei,2*ti+1,l,r);
    node res=merge(lft,rgt);
    return res;

}
void bt(int *arr,node *tree,int si,int ei,int ti){
    if(si==ei){
        tree[ti].maxsum=arr[si];
        tree[ti].sum=arr[si];
        tree[ti].bps=arr[si];
        tree[ti].bss=arr[si];
        return;
    }
    int mid=(si+ei)/2;
    bt(arr,tree,si,mid,2*ti);
    bt(arr,tree,mid+1,ei,2*ti+1);
    tree[ti]=merge(tree[ti*2],tree[2*ti+1]);
    return;
}
int main() {
int n;cin>>n;
    int *arr=new int[50005];
    node *tree=new node[3*50005];
    for(int i=0;i<n;i++){
      cin>>arr[i];
    }
    int t;cin>>t;
    bt(arr,tree,0,n-1,1);
    while(t--){
    int l,r;cin>>l>>r;
    node res=querry(arr,tree,0,n-1,1,l-1,r-1);
    cout<<res.maxsum<<endl;
    }
}