Submission #410975

#	Time	Username	Problem	Language	Result	Execution time	Memory
410975		Kevin_Zhang_TW	Ancient Books (IOI17_books)	C++17	100 / 100	134 ms	14916 KiB

books

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define pb emplace_back
#define AI(i) begin(i), end(i)
template<class T> bool chmin(T &a, T b) { return b < a && (a = b, true); }
template<class T> bool chmax(T &a, T b) { return a < b && (a = b, true); }
#ifdef KEV
#define DE(args...) kout("[ " + string(#args) + " ] = ", args)
void kout() { cerr << endl; }
template<class T, class ...U> void kout(T a, U ...b) { cerr << a << ' ', kout(b...); }
void debug(auto l, auto r) { while (l != r) cerr << *l << " \n"[next(l)==r], ++l; }
#else
#define DE(...) 0
#define debug(...) 0
#endif
#include "books.h"

long long minimum_walk(std::vector<int> p, int s) {
	int n = p.size();
	ll res = 0;
	for (int i = 0;i < n;++i)
		res += abs(i - p[i]);

	if (res == 0) return 0;

	int L = 0, R = n-1;
	while (p[L] == L) ++L;
	while (p[R] == R) --R;

	chmax(R, s), chmin(L, s);

	auto expand = [&](int &l, int &r) {
		int nl = l, nr = r;
		auto upd = [&](int pos) {
			chmax(nr, p[pos]);
			chmin(nl, p[pos]);
		};
		upd(l), upd(r);

		while (nl < l || r < nr) {
			while (nl < l) {
				upd(--l);
			}
			while (r < nr) {
				upd(++r);
			}
		}

	};

	int l = s, r = s;
	expand(l, r);

	assert(l >= L && r <= R);

	while (L < l || r < R) {
		int costl = 0, costr = 0;
		int l_l = l, l_r = r;
		int r_l = l, r_r = r;

		bool nxt_l = false;
		{
			int &sl = l_l, &sr = l_r;
			while (sl > L && sr <= r) {
				expand(--sl, sr);
				costl += 2;
			}
			nxt_l = sr > r;
		}
		bool nxt_r = false;
		{
			int &sl = r_l, &sr = r_r;
			while (sl >= l && sr < R) {
				expand(sl, ++sr);
				costr += 2;
			}
			nxt_r = sl < l;
		}
		assert(nxt_r == nxt_l);
		if (nxt_r) {
			res += min(costl, costr);
			assert(l_l == r_l);
			assert(l_r == r_r);
		}
		else {
			res += costl + costr;
			assert(l_l == L && r_r == R);
		}
		l = min(l_l, r_l), r = max(l_r, r_r);
	}

	return res;
}

• Subtask 1: 12 / 12
• Subtask 2: 10 / 10
• Subtask 3: 28 / 28
• Subtask 4: 20 / 20
• Subtask 5: 30 / 30