Submission #1239452

#	Time	Username	Problem	Language	Result	Execution time	Memory
1239452		trantrungkein	Monochrome Points (JOI20_monochrome)	C++20	100 / 100	772 ms	14324 KiB

monochrome

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N = 4e5 + 6;
string s; int n,bi = 0, wi = 0, b[N],w[N],BIT[N];
void update(int id)
{
    for(;id <= 2*n; id += (-id)&id) BIT[id] += 1;
}
int sum(int id)
{
    int res = 0;
    for(;id > 0; id -= (-id)&id) res += BIT[id];
    return res;
}
int get(int l, int r)
{
    return (sum(r) - sum(l-1));
}
int cal(int k)
{
    vector<pair<int,int>> edge;
    memset(BIT,0,sizeof(BIT));
    for(int i = 0; i < n; i++)
    {
        int c = min(w[i],b[(i+k)%n]) , d = max(w[i],b[(i+k)%n]);
        edge.push_back({c,d});
    }
    sort(edge.begin(),edge.end());
    int res = 0;
    for(auto [l,r] : edge)
    {
        res += get(l+1,r+1);
        update(r+1);
    }
    return res;
}
double max_f(double left, double right) {

    double N_ITER = 500;
    for (double i = 0; i < N_ITER; i++) {

        double x1 = left + (right - left) / 3.0;
        double x2 = right - (right - left) / 3.0;

        if (cal(x1) > cal(x2)) right = x2;
        else left = x1;
    }
    return cal(left);
}
main()
{

    cin >> n >> s;
    for(int i = 0; i < 2*n; i++)
    {
        if(s[i] == 'W') w[wi++] = i;
        else b[bi++] = i;
    }
    int left = 0, right = n - 1, mid, ans = 0;
	while(left <= right){
		mid = (right - left) / 2 + left;
		int curr = cal( mid);
		int prev = 0;
		if (mid - 1 >= 0){
			prev = cal( mid - 1);
		}

		ans = max(ans, curr);
		if (curr > prev){
			left = mid + 1;
		}
		else{
			right = mid - 1;
		}
	}
	ans = max(ans, cal( 0));
	ans = max(ans, cal( n - 1));
	cout << ans << "\n";
}

Compilation message (stderr)

monochrome.cpp:51:1: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
   51 | main()
      | ^~~~

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