Dynamic Range Minimum Queries

#include <iostream>
#include <vector>
using namespace std;
#define ll long long
struct SegmentTreeNode {
    int start, end,sum;
    SegmentTreeNode* left;
    SegmentTreeNode* right;
    SegmentTreeNode(int a, int b):start(a),end(b),sum(0),left(nullptr),right(nullptr){}
};



SegmentTreeNode* buildTree(vector<int> &nums, int start, int end) {
    if(start > end) return nullptr;
    SegmentTreeNode* root = new SegmentTreeNode(start,end);
    if(start == end) {
        root->sum = nums[start];
        return root;
    }
    int mid = start + (end - start) / 2;
    root->left = buildTree(nums,start,mid);
    root->right = buildTree(nums,mid+1,end);
    root->sum = min(root->left->sum,root->right->sum);
    return root;
}
int queryTree(int i, int j, SegmentTreeNode* root) {
    if(root == nullptr) return 0;
    if(root->start == i && root->end == j) return root->sum;
    int mid = (root->start + root->end) / 2;
    if(i > mid) return queryTree(i,j,root->right);
    if(j <= mid) return queryTree(i,j,root->left);
    return min(queryTree(i,mid,root->left),queryTree(mid+1,j,root->right));
}
int modifyTree(int i, int val, SegmentTreeNode* root) {
    if(root == nullptr) return 0;

    if(root->start == i && root->end == i) {
        root->sum=val;
        return val;
    }
    int mid = (root->start + root->end) / 2;
    if(i > mid) {
        int value=modifyTree(i,val,root->right);
        root->right->sum = min(root->right->sum,value);
    } else {
        int value=modifyTree(i,val,root->left);
        root->left->sum = min(root->left->sum,value);
    }
    root->sum = min(root->right->sum,root->left->sum);
    return root->sum;
}

int main()
{
   int q,n,a,t,b;
   cin>>n>>q;
   vector<int>v(n);
   for(int i=0;i<n;i++)cin>>v[i];
   SegmentTreeNode* root=buildTree(v,0,n-1);
   while(q--){
       cin>>t>>a>>b;
       if(t==2)cout<<queryTree(a-1,b-1,root)<<endl;
       else modifyTree(a-1,b,root);
   }
   return 0;
}