Submission #633419

#	Time	Username	Problem	Language	Result	Execution time	Memory
633419		Lawliet	Radio Towers (IOI22_towers)	C++17	18 / 100	966 ms	8096 KiB

towers

#include "towers.h"
#include <bits/stdc++.h>

using namespace std;

const int maxl = 20;
const int maxn = 100010;
const int inf = 1000000010;

class SparseTable
{
    public:

        void build(int n, vector<int> v)
        {
            for(int i = 1 ; i <= n ; i++)
                tab[0][i] = v[i];

            for(int k = 1 ; k < maxl ; k++)
                for(int i = 1 ; i + (1 << k) - 1 <= n ; i++)
                    tab[k][i] = max( tab[k - 1][i] , tab[k - 1][i + (1 << (k - 1))] ); 
        }

        int query(int l, int r)
        {
            if( l > r )
                return -inf;

            int t = 31 - __builtin_clz(r - l + 1);
            return max( tab[t][l] , tab[t][r - (1 << t) + 1] );
        }

    protected:

        int tab[maxl][maxn];
};

int n;

int v[maxn];
int dp[maxn];

bool hasBuilt = false;

SparseTable st;

vector<int> valleys;

bool isValid(int i, int j, int D)
{
    int peak = st.query( i + 1 , j - 1 );

    if( v[i] <= peak - D && v[j] <= peak - D )
        return true;

    return false;
}

void build(int D)
{
    for(int i = 1 ; i <= n ; i++)
    {
        while( !valleys.empty() )
        {
            int j = valleys.back();

            if( isValid( j , i , D ) )
            {
                valleys.push_back( i );
                break;
            }

            if( v[j] < v[i] )
                break;

            valleys.pop_back();
        }

        if( valleys.empty() )
            valleys.push_back( i );
    }

    hasBuilt = true;
}

void init(int N, vector<int> H) {
    n = N;

    H.insert( H.begin() , 0 );

    for(int i = 1 ; i <= n ; i++)
        v[i] = H[i];

    st.build( n , H );
}

int max_towers(int L, int R, int D) 
{
    if( !hasBuilt )
        build( D );

    L++; R++;

    if( R - L + 1 <= 2 )
        return 1;

    int pL = lower_bound( valleys.begin() , valleys.end() , L ) - valleys.begin();
    int pR = upper_bound( valleys.begin() , valleys.end() , R ) - valleys.begin();

    if( pL == pR )
    {
        if( isValid( L , R , D ) )
            return 2;

        return 1;
    }

    int ans = pR - pL;

    if( isValid( L , valleys[pL] , D ) )
        ans++;

    if( isValid( valleys[pR - 1] , R , D ) )
        ans++;

    return ans;
}

• Subtask 1: 4 / 4
• Subtask 2: 0 / 11
• Subtask 3: 0 / 12
• Subtask 4: 14 / 14
• Subtask 5: 0 / 17
• Subtask 6: 0 / 19
• Subtask 7: 0 / 23