Submission #628453

#	Time	Username	Problem	Language	Result	Execution time	Memory
628453		MohamedFaresNebili	Monochrome Points (JOI20_monochrome)	C++14	100 / 100	1353 ms	23508 KiB

monochrome

#include <bits/stdc++.h>

            using namespace std;

            using ll = long long;
            using ld = long double;
            using pi = pair<pair<int, int>, pair<int, int>>;

            #define ff first
            #define ss second
            #define pb push_back
            #define all(x) (x).begin(), (x).end()
            #define lb lower_bound
            #define int ll

            int N, ST[800005]; string S;
            vector<int> A, B;
            void update(int p, int v) {
                for(; p <= 2 * N; p += (p & (-p)))
                    ST[p] += v;
            }
            int query(int p) {
                int res = 0;
                for(; p; p -= (p & (-p)))
                    res += ST[p];
                return res;
            }
            int query(int lo, int hi) {
                return query(hi) - query(lo - 1);
            }

            int solve(int v) {
                vector<pair<int, int>> P;
                for(int l = 0; l < N; l++)
                    P.push_back({A[l], B[(l + v) % N]});
                int arr[2 * N]{0};
                for(int l = 0; l < N; l++) {
                    arr[A[l]] = l, arr[B[(l + v) % N]] = l;
                }
                for(int l = 0; l <= 2 * N; l++) ST[l] = 0;
                int res = 0; unordered_map<int, int> M;
                for(int l = 0; l < 2 * N; l++) {
                    if(M.find(arr[l]) != M.end()) {
                        int i = M[arr[l]];
                        update(i, -1); res += query(i, l + 1);
                        continue;
                    }
                    update(l + 1, 1); M[arr[l]] = l + 1;
                }
                return res;
            }

            int32_t main() {
                ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
                cin >> N >> S; int res = 0;
                for(int l = 0; l < 2 * N; l++) {
                    if(S[l] == 'B') A.push_back(l);
                    if(S[l] == 'W') B.push_back(l);
                }
                int lo = 0, hi = N - 1;
                while(lo <= hi) {
                    int md = (lo + hi) / 2;
                    int U = solve(md), V = solve(md + 1);
                    if(V > U) { lo = md + 1, res = max(res, V); }
                    else hi = md - 1, res = max(res, U);
                }
                cout << res << "\n";
                return 0;
            }

• Subtask 1: 4 / 4
• Subtask 2: 21 / 21
• Subtask 3: 10 / 10
• Subtask 4: 65 / 65