Submission #1233661

#	Time	Username	Problem	Language	Result	Execution time	Memory
1233661		coin_	Watching (JOI13_watching)	C++20	100 / 100	570 ms	30444 KiB

watching

#include <bits/stdc++.h>
#define endl '\n'
#define int long long
#define fi first
#define se second
#define pb push_back
using namespace std;

bool check(int n, int p, int q, vector<int> a, int w){
    vector<vector<int>> dp(n+5, vector<int>(p+5, 0));
    dp[0][0] = 1;
    for (int i = 1; i < n; i++){
        int lastSmall = 0, lastBig = 0;
        for (int j = 0; j <= i; j++){
            if (a[i] - a[j] >= w){
                lastSmall++;
            }
            else{
                break;
            }
        }
        for (int j = 0; j <= i; j++){
            if (a[i] - a[j] >= 2*w){
                lastBig++;
            }
            else{
                break;
            }
        }
        // no small cams, forced to use big
        dp[i][0] = (lastBig == 0 ? 1LL : dp[lastBig-1][0] + 1LL);
        for (int j = 1; j <= p; j++){
            if (lastSmall == 0){
                // place 1 small camera, will definitely have 1 small cam availible => 0 large cams
                dp[i][j] = 0LL;
            }
            else if (lastBig == 0){
                // either use 1 large camera or use 1 small cam
                dp[i][j] = min(dp[lastSmall-1][j-1], 1LL);
            }
            else dp[i][j] = min(dp[lastSmall-1][j-1], dp[lastBig-1][j] + 1);
        }
    }
    int ans = 100000000;
    for (int i = 0; i <= p; i++){
        ans = min(ans, dp[n-1][i]);
    }
    return ans <= q;
}
 
signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    int t = 1;
    // cin >> t;
    while(t--){
        // p - small, q - large
        int n, p, q;
        cin >> n >> p >> q;
        vector<int> a(n);
        for (int i = 0; i < n; i++){
            cin >> a[i];
        }
        sort(a.begin(), a.end());
        if (p + q >= n){
            cout << 1;
            break;
        }
        int l = 1, r = 1000000001;
        while(l < r){
            int mid = (l + r) / 2;
            if (check(n, p, q, a, mid)){
                r = mid;
            }
            else{
                l = mid + 1;
            }
        }
        cout << r;
    }
}

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