Submission #292892

#	Time	Username	Problem	Language	Result	Execution time	Memory
292892		limabeans	Monochrome Points (JOI20_monochrome)	C++17	4 / 100	2073 ms	384 KiB

monochrome

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

template<typename T>
void out(T x) { cout << x << endl; exit(0); }
#define watch(x) cout << (#x) << " is " << (x) << endl





using ll = long long;

const ll mod = 1e9+7;
const int maxn = 1e6 + 5;




int n;
string s;
bool used[maxn];
vector<pair<int,int>> v;
int best=0;



bool isect(pair<int,int> p, pair<int,int> q) {
    if (max(p.first,q.first) >= min(p.second,q.second)) return false;
    if (p.first>q.first) swap(p,q);
    if (p.first<=q.first && q.second<=p.second) return false;
    return true;
}

void eval() {
    assert(int(v.size())==n/2);
    for (auto &p: v) {
	if (p.first>p.second) {
	    swap(p.first,p.second);
	}
    }
    int res = 0;
    
    for (int i=0; i<n/2; i++) {
	for (int j=i+1; j<n/2; j++) {
	    if (isect(v[i],v[j])) res++;
	}
    }

    // watch(res);
    // for (auto p: v) {
    // 	cout<<p.first<<" "<<p.second<<endl;
    // }

    best = max(best, res);
}

void dfs(int i) {
    if (i == n) {
	eval();
    } else {
	if (s[i]=='B') {
	    for (int j=0; j<n; j++) {
		if (s[j]=='W') {
		    if (!used[j]) {
			used[j]=true;
			v.push_back({i,j});
			dfs(i+1);
			v.pop_back();
			used[j]=false;
		    }
		}
	    }
	} else {
	    dfs(i+1);
	}
    }
}

int main() {
    ios_base::sync_with_stdio(false); cin.tie(0);  cout.tie(0);
    cin>>n>>s;
    n *= 2;
    dfs(0);
    
    cout<<best<<endl;    
    return 0;
}

• Subtask 1: 4 / 4
• Subtask 2: 0 / 21
• Subtask 3: 0 / 10
• Subtask 4: 0 / 65