Submission #855467

#	Time	Username	Problem	Language	Result	Execution time	Memory
855467		RiverFlow	Watching (JOI13_watching)	C++14	100 / 100	136 ms	16472 KiB

watching

#include <bits/stdc++.h>

#define nl "\n"
#define no "NO"
#define yes "YES"
#define fi first
#define se second
#define vec vector
#define task "main"
#define _mp make_pair
#define ii pair<int, int>
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define evoid(val) return void(std::cout << val)
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FOD(i, b, a) for(int i = (b); i >= (a); --i)
#define unq(x) sort(all(x)); x.resize(unique(all(x)) - x.begin())

using namespace std;

template<typename U, typename V> bool maxi(U &a, V b) {
    if (a < b) { a = b; return 1; } return 0;
}
template<typename U, typename V> bool mini(U &a, V b) {
    if (a > b || a == -1) { a = b; return 1; } return 0;
}

const int N = (int)2e3 + 9;
const int mod = (int)1e9 + 7;

void prepare(); void main_code();

int main() {
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    if (fopen(task".inp", "r")) {
        freopen(task".inp", "r", stdin);
        freopen(task".out", "w", stdout);
    }
    const bool MULTITEST = 0; prepare();
    int num_test = 1; if (MULTITEST) cin >> num_test;
    while (num_test--) { main_code(); }
}

void prepare() {};

int dp[N][N], a[N], nxt1[N], nxt2[N];

void main_code() {
    int n, p, q; cin >> n >> p >> q;

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

    sort(a + 1, a + n + 1);

    if (p + q >= n) evoid(1);
    // binary search w

    // dp[i][j] => min k have used so that cover first i point

    // j : number of small camera used

    int l = 1, r = (int)1e9 + 100, ans = -1;

    while (l <= r) {
        int m = (l + r) >> 1, w = m;
        memset(dp, -1, sizeof dp); dp[0][0] = 0;
        int j = 0; FOR(i, 1, n) {
            while (j + 1 <= n and a[j + 1] - a[i] + 1 <= w) ++j;
            nxt1[i] = j;
        }
        j = 0; FOR(i, 1, n) {
             while (j + 1 <= n and (a[j + 1] - a[i] + 2) / 2 <= w) ++j;
            nxt2[i] = j;
        }
        FOR(i, 0, n - 1) FOR(j, 0, p) if (dp[i][j] != -1) {
            if (j + 1 <= p)
                mini(dp[nxt1[i + 1]][j + 1], dp[i][j]);
            mini(dp[nxt2[i + 1]][j], dp[i][j] + 1);
        }
        bool ok = 0;
        FOR(j, 0, p) if (dp[n][j] != -1 and dp[n][j] <= q) {
            ok = 1; break ;
        }
        if (ok) {
            ans = m; r = m - 1;
        } else
            l = m + 1;
    }

    cout << ans;
}


/*     Let the river flows naturally     */

Compilation message (stderr)

watching.cpp: In function 'int main()':
watching.cpp:36:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   36 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
watching.cpp:37:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   37 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 50 / 50
• Subtask 2: 50 / 50