Submission #1293120

#	Time	Username	Problem	Language	Result	Execution time	Memory
1293120		thaibeo123	Watching (JOI13_watching)	C++20	100 / 100	80 ms	14288 KiB

watching

#include <bits/stdc++.h>
using namespace std;

#define NAME "A"
#define ll long long
#define fi first
#define se second
#define pb push_back
#define all(x) x.begin(), x.end()
#define MASK(x) (1ll << (x))
#define BIT(x, i) (((x) >> (i)) & 1)

const int N = 2005;
const int inf = 1e9;

int n, p, q;
int a[N], pos[N][2];
int dp[N][N];

bool f(int w) {
    for (int i = 1; i <= n; i++) {
        pos[i][0] = upper_bound(a + 1, a + 1 + n, a[i] + w - 1) - a - 1;
        pos[i][1] = upper_bound(a + 1, a + 1 + n, a[i] + 2 * w - 1) - a - 1;
    }
    for (int i = 1; i <= n; i++) {
        for (int j = 0; j <= i; j++) {
            dp[i][j] = inf;
        }
    }
    dp[0][0] = 0;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j <= min(i, p); j++) {
            if (dp[i][j] == inf) continue;
            if (j + 1 <= p) {
                if (pos[i + 1][0] >= n) return 1;
                dp[pos[i + 1][0]][j + 1] = min(dp[pos[i + 1][0]][j + 1], dp[i][j]);
            }
            if (dp[i][j] + 1 <= q) {
                if (pos[i + 1][1] >= n) return 1;
                dp[pos[i + 1][1]][j] = min(dp[pos[i + 1][1]][j], dp[i][j] + 1);
            }
        }
    }
    return 0;
}

void input() {
    cin >> n >> p >> q;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
    }
    sort(a + 1, a + 1 + n);
}

void solve() {
    if (p + q >= n) {
        cout << 1;
        return;
    }
    int l = 1, r = 1e9, ans = 1e9;
    while (l <= r) {
        int mid = (l + r) >> 1;
        if (f(mid)) {
            ans = mid;
            r = mid - 1;
        }
        else {
            l = mid + 1;
        }
    }
    cout << ans;
}

signed main() {
    if (fopen(NAME".INP", "r")) {
        freopen(NAME".INP", "r", stdin);
        freopen(NAME".OUT", "w", stdout);
    }
    cin.tie(0)->sync_with_stdio(0);

    input();
    solve();

    return 0;
}

Compilation message (stderr)

watching.cpp: In function 'int main()':
watching.cpp:76:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   76 |         freopen(NAME".INP", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
watching.cpp:77:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   77 |         freopen(NAME".OUT", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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