Submission #502677

#	Time	Username	Problem	Language	Result	Execution time	Memory
502677		Sad_Bus	Watching (JOI13_watching)	C++14	50 / 100	1087 ms	32080 KiB

watching

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

long long get_rand() {
    long long a = rand();
    long long b = rand();
    return a * (RAND_MAX + 1ll) + b;
}

#define int long long
#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
#define ordered_multiset tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update>
#define intmin -100000000000000000LL
#define intmax 100000000000000000LL

vector<int> arr;
int n, p, q;

bool check(int m){
    //I will require total at most n cameras
    vector<vector<int>> dp(n+2, vector<int>(n+2, 0)); //position, small cameras, will be at most n

    for (int i = 1; i <= n; ++i)
    {
        int sOne = lower_bound(arr.begin(), arr.end(), arr[i]-(2*m)+1) - arr.begin();
        dp[i][0] = dp[max(0LL, sOne-1)][0] + 1;
        for (int j = 1; j <= min(p, i); ++j) //use those many small cameras max
        {
            //first position behind ith with diff <= m, aka use a small camera;
            int one = lower_bound(arr.begin(), arr.end(), arr[i]-m+1) - arr.begin() - 1;
            one = max(0LL, one);

            //first position behind ith with diff <= 2*m, aka use a big camera;
            int two = lower_bound(arr.begin(), arr.end(), arr[i]-(m*2)+1) - arr.begin() - 1;
            two = max(0LL, two);

            dp[i][j] = min(dp[one][j-1], dp[two][j]+1);
        }
    }

    for (int i = 0; i <= min(p, n); ++i)
    {
        if(dp[n][i] <= q){
            return true;
        }
    }

    return false;
}

int32_t main(){
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

    cin >> n >> p >> q;

    arr.assign(n+1, 0);
    arr[0] = 0;
    for (int i = 1; i <= n; ++i)
    {
        cin >> arr[i];
    }
    sort(arr.begin(), arr.end());

    int l = 0, r = 10000000000, mid = (l+r)/2, ans;
    while(l <= r){
        mid = (l+r)/2;
        if(check(mid)){
            ans = mid;
            r = mid - 1;
        }
        else{
            l = mid + 1;
        }
    }

    cout << max(ans, 1LL) << '\n';
}

Compilation message (stderr)

watching.cpp: In function 'int32_t main()':
watching.cpp:70:48: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized]
   70 |     int l = 0, r = 10000000000, mid = (l+r)/2, ans;
      |                                                ^~~

• Subtask 1: 50 / 50
• Subtask 2: 0 / 50