Submission #425432

#	Time	Username	Problem	Language	Result	Execution time	Memory
425432		Kevin_Zhang_TW	Sparklers (JOI17_sparklers)	C++17	50 / 100	28 ms	1328 KiB

sparklers

#include<bits/stdc++.h>
#define pb emplace_back
#define AI(i) begin(i), end(i)
using namespace std;
using ll = long long;
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 v, U ...e) { cerr << v << ' ', kout(e...); }
template<class T> void debug(T L, T R) { while (L != R) cerr << *L << " \n"[next(L)==R], ++L; }
#else
#define DE(...) 0
#define debug(...) 0
#endif
// What I should check
// 1. overflow
// 2. corner cases
// Enjoy the problem instead of hurrying to AC
// Good luck !
const int MAX_N = 1010;
 
const ll inf = 1ll << 55;
 
int n, k, T;
int pos[MAX_N];
 
bool dp[MAX_N][MAX_N];
ll a[MAX_N];

bool valid(ll S) {
	memset(dp, 0, sizeof(dp));

	dp[k][k] = true;

	for (int i = 1;i <= n;++i) {
		a[i] = 2 * S * T * i - pos[i];
	}

	for (int l = k;l >= 1;--l)
		for (int r = k;r <= n;++r) {

			auto valid = [&](int l, int r) {
				return a[l] <= a[r];
				//return 2 * S * (r-l) * T >= (pos[r] - pos[l]);
			};
			
			if (dp[l][r]) {
				if (r < n) {
					ll d = pos[r+1] - pos[r];
					if (valid(l, r+1))
						dp[l][r+1] = true;
				}
				if (l > 1) {
					ll d = pos[l] - pos[l-1];
					if (valid(l-1, r))
						dp[l-1][r] = true;
				}
			}
		}

	return dp[1][n];
}
 
int32_t main() {
	ios_base::sync_with_stdio(0), cin.tie(0);
	cin >> n >> k >> T;
	for (int i = 1;i <= n;++i)
		cin >> pos[i];

	//assert(n < MAX_N);
 
	ll L = 0, R = 2 * pos[n], M;
 
	while (L < R) {
		M = L + R >> 1;
		if (valid(M))
			R = M;
		else L = M + 1;
	}
 
	cout << L << '\n';
	
}

Compilation message (stderr)

sparklers.cpp: In function 'bool valid(ll)':
sparklers.cpp:51:9: warning: unused variable 'd' [-Wunused-variable]
   51 |      ll d = pos[r+1] - pos[r];
      |         ^
sparklers.cpp:56:9: warning: unused variable 'd' [-Wunused-variable]
   56 |      ll d = pos[l] - pos[l-1];
      |         ^
sparklers.cpp: In function 'int32_t main()':
sparklers.cpp:77:9: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   77 |   M = L + R >> 1;
      |       ~~^~~

• Subtask 1: 30 / 30
• Subtask 2: 20 / 20
• Subtask 3: 0 / 50