Submission #1080424

#	Time	Username	Problem	Language	Result	Execution time	Memory
1080424		isaachew	Sparklers (JOI17_sparklers)	C++17	50 / 100	122 ms	262144 KiB

sparklers

#include <bits/stdc++.h>
/*
 The sparkler should move in both directions from the initial person after it is lit
 
 If two people meet, they should do so as soon as possible, otherwise it wouldn't make a difference
 
 A path actually depends on the sum of distances of the first and last people from the person with the sparkler
 
 */
int main(){
    std::ios::sync_with_stdio(0);
    std::cin.tie(0);
    long long n,k,t;
    std::cin>>n>>k>>t;
    k--;
    std::vector<int> places;
    for(int i=0;i<n;i++){
        int a;
        std::cin>>a;
        places.push_back(a);
    }
    long long lower=-1,upper=1e9;//min distance a sparkler can burn for
    //I forgot 0
    while(lower+1<upper){
        long long mid=(lower+upper)/2;
        std::vector<std::vector<int>> dp(n,std::vector<int>(n));
        dp[k][k]=1;
        for(int i=0;i<n-1;i++){
            for(int l=0;l+i<n;l++){
                int r=l+i;
                if(dp[l][r]){
                    if(r+1<n&&places[r+1]-places[l]<=mid*(i+1)){
                        dp[l][r+1]=1;
                    }
                    if(l&&places[r]-places[l-1]<=mid*(i+1)){
                        dp[l-1][r]=1;
                    }
                }
            }
        }
        if(dp[0][n-1]){
            upper=mid;
        }else{
            lower=mid;
        }
    }
    //std::cout<<upper<<'\n';
    //upper/=2;//towards each other
    std::cout<<(upper+2*t-1)/(2*t)<<'\n';
}

• Subtask 1: 30 / 30
• Subtask 2: 20 / 20
• Subtask 3: 0 / 50