Submission #1087073

#	Time	Username	Problem	Language	Result	Execution time	Memory
1087073		pokmui9909	Sparklers (JOI17_sparklers)	C++17	100 / 100	28 ms	3052 KiB

sparklers

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

ll N, K, T, A[100005], B[100005];

bool f(ll v){
    for(ll i = 1; i <= N; i++){
        B[i] = A[i] - 2 * v * T * i;
    }
    ll gl = K, gr = K;
    for(ll i = 1; i <= N; i++){
        if(i <= K && B[gl] <= B[i]) gl = i;
        if(i >= K && B[gr] >= B[i]) gr = i;
    }
    ll l = K, r = K;
    while(1){
        ll ch = 0, nl = l, nr = r;
        while(nl > gl && B[nl - 1] >= B[r] && (nl == l || B[nl] < B[l])) nl--;
        if(B[nl] >= B[l] && nl < l){
            l = nl, ch = 1;
        }

        while(nr < gr && B[nr + 1] <= B[l] && (nr == r || B[nr] > B[r])) nr++;
        if(B[nr] <= B[r] && nr > r){
            r = nr, ch = 1;
        }
        if(ch == 0) break;
    }
    if(l != gl || r != gr) return 0;
    l = 1, r = N;
    if(B[l] < B[r]) return 0;
    while(1){
        ll ch = 0, nl = l, nr = r;
        while(nl < gl && B[nl + 1] >= B[r] && (nl == l || B[nl] < B[l])) nl++;
        if(B[nl] >= B[l] && nl > l){
            l = nl, ch = 1;
        }

        while(nr > gr && B[nr - 1] <= B[l] && (nr == r || B[nr] > B[r])) nr--;
        if(B[nr] <= B[r] && nr < r){
            r = nr, ch = 1;
        }
        if(ch == 0) break;
    }
    return (l == gl && r == gr);
}

int main(){
    cin.tie(0) -> sync_with_stdio(0);

    cin >> N >> K >> T;
    for(ll i = 1; i <= N; i++){
        cin >> A[i];
    }
    if(A[N] == 0){
        cout << 0; return 0;
    }
    ll L = 1, R = 1e9;
    while(L <= R){
        ll m = (L + R) / 2;
        if(f(m)) R = m - 1;
        else L = m + 1;
    }
    cout << L;
}

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