CSES – Array Division

#include<bits/stdc++.h>
#define int long long
#define double long double
#define f first
#define s second
#define fastio ios_base::sync_with_stdio(false);cin.tie(0)
using namespace std;
int n,k;
vector<int>a;
bool check(int m){
    int cur = 0, cnt = 1;
    for(int i=0;i<n;i++){
        if(cur + a[i] > m){
            cnt++;
            cur = 0;
        }
        cur += a[i];
    }
    return cnt <= k;
}
signed main(){
    fastio;
    cin>>n>>k;
    int sm = 0;
    int maxx = -1e18;
    for(int i=0;i<n;i++){
        int x; cin>>x;
        a.push_back(x);
        sm += x;
        maxx = max(maxx,x);
    }
    int L = maxx-1, R = sm+1;
    while(R-L > 1){
        int m = L+(R-L)/2;
        if(check(m)) R = m;
        else L = m;
    }
    cout<<R<<"\n";
    return 0;
}