Submission #1174172

#	Time	Username	Problem	Language	Result	Execution time	Memory
1174172		InvMOD	Global Warming (CEOI18_glo)	C++20	100 / 100	37 ms	3780 KiB

glo

#include<bits/stdc++.h>

using namespace std;

#define sz(v) (int)(v).size()
#define all(v) (v).begin(), (v).end()

void solve()
{
    int n,x; cin >> n >> x;

    vector<int> a(n + 1);
    for(int i = 1; i <= n; i++){
        cin >> a[i];
    }

    /*
        + it's optimal to increase / decrease prefix or suffix of array
        + increase is the same as decrease
        + -> prefix LIS and suffix LDS <(")
    */

    vector<int> lis, pref(n + 1), suf(n + 1);
    for(int i = 1; i <= n; i++){
        if(!sz(lis)){
            pref[i] = 1;
            lis.push_back(a[i]);
        }
        else{
            int p = lower_bound(all(lis), a[i]) - lis.begin();
            pref[i] = p + 1;

            if(p == sz(lis)){
                lis.push_back(a[i]);
            }
            else lis[p] = a[i];
        }
    }

    vector<int> lds;
    for(int i = n; i >= 1; i--){
        if(!sz(lds)){
            suf[i] = 1;
            // increase all suffix by x
            lds.push_back(-(a[i] + x));
        }
        else{
            int place_i = lower_bound(all(lds), -a[i]) - lds.begin() - 1;
            suf[i] = place_i + 2;

            int p = lower_bound(all(lds), -(a[i] + x)) - lds.begin();
            if(p == sz(lds)){
                lds.push_back(-(a[i] + x));
            }
            else lds[p] = -(a[i] + x);
        }
    }

    int answer = 0;
    for(int i = 1; i <= n; i++){
        answer = max(answer, pref[i] + suf[i] - 1);
    }

    cout << answer << "\n";
}

int32_t main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);

    #define name "InvMOD"
    if(fopen(name".INP", "r")){
        freopen(name".INP", "r", stdin);
        freopen(name".OUT", "w", stdout);
    }

    solve();
    return 0;
}

Compilation message (stderr)

glo.cpp: In function 'int32_t main()':
glo.cpp:73:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   73 |         freopen(name".INP", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
glo.cpp:74:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   74 |         freopen(name".OUT", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 5 / 5
• Subtask 2: 10 / 10
• Subtask 3: 13 / 13
• Subtask 4: 10 / 10
• Subtask 5: 20 / 20
• Subtask 6: 17 / 17
• Subtask 7: 25 / 25