Submission #1095917

#	Time	Username	Problem	Language	Result	Execution time	Memory
1095917		_8_8_	Monochrome Points (JOI20_monochrome)	C++17	100 / 100	391 ms	7908 KiB

monochrome

#include <bits/stdc++.h>
    
using namespace std;
    
typedef long long ll;
const int  N = 2e5 + 12, MOD = (int)1e9 + 7;

int n, t[N * 2], val[N * 2];
string s;
vector<int> x, y;
void add(int i, int val) {
    while(i <= n + n) {
        t[i] += val;
        i += i & -i;
    }
}
ll get(int i) {
    ll ret = 0;
    while(i) {
        ret += t[i];
        i -= i & -i;
    }
    return ret;
}
ll get(int l, int r) {
    return get(r) - get(l - 1);
}
ll mem[N];
ll calc(int k) {
    if(mem[k] != -1) {
        return mem[k];
    }
    for(int i = 1; i <= n + n; i++) {
        t[i] = 0;
    }
    ll ret = 0;
    for(int i = 0; i < n; i++) {
        int j = (i + k) % n;
        int l = x[i], r = y[j];
        if(l > r) {
            swap(l, r);
        }
        val[l] = -1;
        val[r] = l;
    }
    for(int x = 1; x <= n + n; x++) {
        int y = val[x];
        if(y == -1) {
            add(x, 1); 
        } else {
            ret += get(y + 1, x);
            add(y, -1);
        }
    }
    return mem[k] = ret;
}
void test() {
    memset(mem, -1, sizeof(mem));
    cin >> n >> s;
    for(int i = 0; i < n + n; i++) {
        if(s[i] == 'W') {
            x.push_back(i + 1);
        } else {
            y.push_back(i + 1);
        }
    }
    if(n == 1) {
        cout << 0 << '\n';
        return;
    }
    if(calc(0) < calc(1)) {
        int l = 1, r = n;
        while(r - l > 1) {
            int mid = (l + r) >> 1;
            if(calc(mid) > calc(mid - 1)) {
                l = mid;
            } else {
                r = mid;
            }
        }
        cout << calc(l) << '\n';
    } else {
        int l = -1, r = n - 1;
        while(r - l > 1) {
            int mid = (l + r) >> 1;
            if(calc(mid) > calc(mid + 1)) {
                r = mid;
            } else {
                l = mid;
            }
        }
        cout << calc(r) << '\n';
    }
}
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0); 

    int t = 1; 
    // cin >> t;
    
    while(t--) 
        test();
    return 0;
}

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