Submission #883603

#	Time	Username	Problem	Language	Result	Execution time	Memory
883603		DAleksa	Sparklers (JOI17_sparklers)	C++17	100 / 100	840 ms	7764 KiB

sparklers

#include <bits/stdc++.h>
 
using namespace std;
 
#define int long long
 
const int N = 1e5 + 10;
int n, k, t;
int a[N];
long long x[N];
set<long long> L, R;
 
signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> k >> t;
    for(int i = 1; i <= n; i++) cin >> a[i];
    int l = 0, r = 1e9;
    int ans = r;
    while(l <= r) {
        int mid = (l + r) / 2;
        if(2LL * mid * t > 1e9) {
            ans = mid;
            r = mid - 1;
            continue;
        }
        for(int i = 1; i <= n; i++) x[i] = a[i] - 2LL * mid * i * t;
        L.clear();
        R.clear();
        L.insert(x[k]);
        R.insert(x[k]);
        int i = k, j = k;
        while(true) {
            int change = 0;
            auto it = R.begin();
            if(i > 1) it = R.upper_bound(x[i - 1]);
            while(i > 1 && it != R.begin()) {
                change++;
                i--;
                L.insert(x[i]);
                if(i > 1) it = R.upper_bound(x[i - 1]);
            }
            if(j < n) it = L.lower_bound(x[j + 1]);
            while(j < n && it != L.end()) {
                change++;
                j++;
                R.insert(x[j]);
                if(j < n) it = L.lower_bound(x[j + 1]);
            }
            if(change == 0) break;
        }
        if(i != 1 || j != n) {
            l = mid + 1;
            continue;
        }
        L.clear();
        R.clear();
        L.insert(x[1]);
        R.insert(x[n]);
        if(x[1] < x[n]) {
            l = mid + 1;
            continue;
        }
        i = 1, j = n;
        while(true) {
            int change = 0;
            auto it = R.begin();
            if(i < k) it = R.upper_bound(x[i + 1]);
            while(i < k && it != R.begin()) {
                change++;
                i++;
                L.insert(x[i]);
                if(i < k) it = R.upper_bound(x[i + 1]);
            }
            if(j > k) it = L.lower_bound(x[j - 1]);
            while(j > k && it != L.end()) {
                change++;
                j--;
                R.insert(x[j]);
                if(j > k) it = L.lower_bound(x[j - 1]);
            }
            if(change == 0) break;
        }
        if(i != k || j != k) {
            l = mid + 1;
            continue;
        }
        ans = mid;
        r = mid - 1;
    }
    cout << ans;
    return 0;
}

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