oj.uz

Submission #735781

# Submission time Handle Problem Language Result Execution time Memory
735781 2023-05-04T16:19:28 Z GrindMachine Election (BOI18_election) C++17
100 / 100
 508 ms 52964 KB 
// Om Namah Shivaya

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x, y) ((x + y - 1) / (y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl

#define rep(i, n) for(int i = 0; i < n; ++i)
#define rep1(i, n) for(int i = 1; i <= n; ++i)
#define rev(i, s, e) for(int i = s; i >= e; --i)
#define trav(i, a) for(auto &i : a)

template<typename T>
void amin(T &a, T b) {
    a = min(a, b);
}

template<typename T>
void amax(T &a, T b) {
    a = max(a, b);
}

#ifdef LOCAL
#include "debug.h"
#else
#define debug(x) 42
#endif

/*

refs:
edi
https://github.com/stefdasca/CompetitiveProgramming/blob/master/BalkanOI/Balkan%2018-Election.cpp


let a[i] = 1 for 'C' and a[i] = -1 for 'T'

if only pref condition is there, then following greedy works:
iterate from l to r, add a[i] to sum
if sum < 0, then ignore curr guy and make sum = 0
add 1 to ans every time this op is done

how to handle suff cond?
first run pref, and find out the guys to ignore
when doing for pref, we make ignore ops as much to the right as possible
so when doing suff ops, this means ignore ops will come earlier
which will benefit the suff

so in short:
run pref, mark guys to ignore
run suff, ignore marked guys and ignore any addl guys if required

how to optimize?

if we can find out all guys ignored in the pref run, then we know the #of ops for the suff run
ops for suff run = -(min suff)

how to find and upd guys ignored in the pref run?

sweepline idea
sweep over l from n to 1

based on the value of a[l] (-1/1), upd the ignored guys
to find min suff after updates, use segtree

*/

const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;

template<typename T>
struct segtree {
    // https://codeforces.com/blog/entry/18051

    /*=======================================================*/

    struct data {
        ll mnsuff, sum;
    };

    data neutral = {0, 0};

    data merge(data &left, data &right) {
        data curr;

        curr.mnsuff = min(right.mnsuff, right.sum + left.mnsuff);
        curr.sum = left.sum + right.sum;

        return curr;
    }

    void create(int i, T v) {
        tr[i] = {min(v, 0ll), v};
    }

    void modify(int i, T v) {
        tr[i] = {min(v, 0ll), v};
    }

    /*=======================================================*/

    int n;
    vector<data> tr;

    segtree() {

    }

    segtree(int siz) {
        init(siz);
    }

    void init(int siz) {
        n = siz;
        tr.assign(2 * n, neutral);
    }

    void build(vector<T> &a, int siz) {
        rep(i, siz) create(i + n, a[i]);
        rev(i, n - 1, 1) tr[i] = merge(tr[i << 1], tr[i << 1 | 1]);
    }

    void pupd(int i, T v) {
        modify(i + n, v);
        for (i = (i + n) >> 1; i; i >>= 1) tr[i] = merge(tr[i << 1], tr[i << 1 | 1]);
    }

    data query(int l, int r) {
        data resl = neutral, resr = neutral;

        for (l += n, r += n; l <= r; l >>= 1, r >>= 1) {
            if (l & 1) resl = merge(resl, tr[l++]);
            if (!(r & 1)) resr = merge(tr[r--], resr);
        }

        return merge(resl, resr);
    }
};

void solve(int test_case)
{
    ll n; cin >> n;
    vector<ll> a(n + 5);
    rep1(i, n) {
        char ch; cin >> ch;
        if (ch == 'C') a[i] = 1;
        else a[i] = -1;
    }

    ll q; cin >> q;
    vector<pll> here[n + 5];

    rep1(i, q) {
        ll l, r; cin >> l >> r;
        here[l].pb({r, i});
    }

    segtree<ll> st(n + 5);
    st.build(a, n + 1);

    deque<ll> dq;
    vector<ll> ans(q + 5);

    rev(l, n, 1) {
        if (a[l] == -1) {
            dq.push_front(l);
            st.pupd(l, 0);
        }
        else {
            if (!dq.empty()) {
                ll i = dq.front();
                st.pupd(i, -1);
                dq.pop_front();
            }
        }

        for (auto [r, id] : here[l]) {
            ll pref_ignored = upper_bound(all(dq), r) - dq.begin();
            ll suff_ignored = -st.query(l, r).mnsuff;
            ans[id] = pref_ignored + suff_ignored;
        }
    }

    rep1(i, q) cout << ans[i] << endl;
}

int main()
{
    fastio;

    int t = 1;
    // cin >> t;

    rep1(i, t) {
        solve(i);
    }

    return 0;
}

Subtask #1
28.0 / 28.0

# Verdict Execution time Memory Grader output
1 Correct 1 ms 468 KB Output is correct
2 Correct 1 ms 468 KB Output is correct
3 Correct 1 ms 468 KB Output is correct
4 Correct 1 ms 468 KB Output is correct
5 Correct 2 ms 468 KB Output is correct

Subtask #2
54.0 / 54.0

# Verdict Execution time Memory Grader output
1 Correct 1 ms 468 KB Output is correct
2 Correct 1 ms 468 KB Output is correct
3 Correct 1 ms 468 KB Output is correct
4 Correct 1 ms 468 KB Output is correct
5 Correct 2 ms 468 KB Output is correct
6 Correct 47 ms 7368 KB Output is correct
7 Correct 35 ms 7256 KB Output is correct
8 Correct 35 ms 7080 KB Output is correct
9 Correct 43 ms 7252 KB Output is correct
10 Correct 40 ms 7252 KB Output is correct
11 Correct 47 ms 7468 KB Output is correct
12 Correct 42 ms 7392 KB Output is correct
13 Correct 49 ms 7628 KB Output is correct
14 Correct 39 ms 7396 KB Output is correct
15 Correct 38 ms 7408 KB Output is correct

Subtask #3
18.0 / 18.0

# Verdict Execution time Memory Grader output
1 Correct 1 ms 468 KB Output is correct
2 Correct 1 ms 468 KB Output is correct
3 Correct 1 ms 468 KB Output is correct
4 Correct 1 ms 468 KB Output is correct
5 Correct 2 ms 468 KB Output is correct
6 Correct 47 ms 7368 KB Output is correct
7 Correct 35 ms 7256 KB Output is correct
8 Correct 35 ms 7080 KB Output is correct
9 Correct 43 ms 7252 KB Output is correct
10 Correct 40 ms 7252 KB Output is correct
11 Correct 47 ms 7468 KB Output is correct
12 Correct 42 ms 7392 KB Output is correct
13 Correct 49 ms 7628 KB Output is correct
14 Correct 39 ms 7396 KB Output is correct
15 Correct 38 ms 7408 KB Output is correct
16 Correct 462 ms 50804 KB Output is correct
17 Correct 304 ms 50464 KB Output is correct
18 Correct 353 ms 49116 KB Output is correct
19 Correct 377 ms 50084 KB Output is correct
20 Correct 433 ms 49848 KB Output is correct
21 Correct 508 ms 52592 KB Output is correct
22 Correct 436 ms 51816 KB Output is correct
23 Correct 488 ms 52964 KB Output is correct
24 Correct 460 ms 52032 KB Output is correct
25 Correct 423 ms 51060 KB Output is correct