Submission #869465

#	Time	Username	Problem	Language	Result	Execution time	Memory
869465		Hakiers	Monochrome Points (JOI20_monochrome)	C++17	35 / 100	300 ms	4304 KiB

monochrome

#include <bits/stdc++.h>
using namespace std;
const int BASE = 1 << 12;
int TREE[BASE << 1];
int n;
string monochrome;
queue<int> BPOS;
queue<int> WPOS;

void add(int v, int val){
	v+=BASE;
	TREE[v] += val;
	v/=2;
	while(v > 0){
		int l = 2*v, r = 2*v+1;
		TREE[v] = TREE[l] + TREE[r];
		v/=2;
	}
}
int query(int a, int b){
	a += BASE - 1;
	b += BASE + 1;
	
	int res = 0;
	while(a/2 != b/2){
		if(!(a&1)) res += TREE[a+1];
		if(b&1) res += TREE[b-1];
		a/=2; b/=2;
	}
	return res;
}

void treeclear(){
	for(int i = 0; i < (BASE << 1); i++)
		TREE[i] = 0;

}

int solve(int wsp){
	treeclear();

	for(int i = n+wsp; i >= 1 + wsp; i--){
		if(monochrome[i] == 'B')
			BPOS.push(i);
		else if(monochrome[i] == 'W')
			WPOS.push(i);
	}
	
	int res = 0;
	
	for(int i = 2*n+wsp; i >= n+1 + wsp; i--){
		if(monochrome[i] == 'B'){
			int v = WPOS.front();
			WPOS.pop();
			//cout << "query: " << query(v, BASE-1) << "\n";
			res += query(v, BASE-1);
			add(v, 1);
		}
		else if(monochrome[i] == 'W'){
			int v = BPOS.front();
			BPOS.pop();
			//cout << "query: " << query(v, BASE-1) << "\n";
			res += query(v, BASE-1);
			add(v, 1);
		}
	}

	return res;
}

int best(){
	int res = 0;
	
	for(int i = 0; i <= n; i++)
		res = max(res, solve(i));
	return res;

}

int main(){
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cin >> n;
	cin >> monochrome;
	monochrome = monochrome + monochrome;
	monochrome = "#" + monochrome;
	
	/*
	for(int i = n; i >= 1; i--){
		if(monochrome[i] == 'B')
			BPOS.push(i);
		else if(monochrome[i] == 'W')
			WPOS.push(i);
	}
	*/
	cout << best() << "\n";

}

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