Submission #516467

#	Time	Username	Problem	Language	Result	Execution time	Memory
516467		qwerasdfzxcl	Monochrome Points (JOI20_monochrome)	C++14	100 / 100	1374 ms	9020 KiB

monochrome

#include <bits/stdc++.h>

typedef long long ll;
using namespace std;
const ll INF = 1e18;
struct Seg{
    int tree[800800], sz;
    void init(int n){
        sz = n;
        fill(tree, tree+sz*2, 0);
    }
    void update(int p, int x){
        for (tree[p+=sz]+=x;p>1;p>>=1) tree[p>>1] = tree[p] + tree[p^1];
    }
    int query(int l, int r){
        int ret = 0;
        for (l+=sz, r+=sz;l<r;l>>=1, r>>=1){
            if (l&1) ret += tree[l++];
            if (r&1) ret += tree[--r];
        }
        return ret;
    }
}tree;
char a[400400];
int B[200200], W[200200], arr[400400];
vector<pair<int, int>> E;

ll calc(int n){
    for (auto &p:E){
        if (p.first > p.second) swap(p.first, p.second);
        arr[p.first] = -1;
        arr[p.second] = p.first;
    }
    tree.init(n+1);

    ll ret = 0;
    for (int i=1;i<=n;i++){
        if (arr[i]==-1) tree.update(i, 1);
        else{
            tree.update(arr[i], -1);
            ret += tree.query(arr[i]+1, i);
        }
    }
    return ret;
}

ll calc2(int n, int z){
    E.clear();
    int pt = z;
    for (int i=1;i<=n/2;i++){
        E.emplace_back(B[i], W[pt]);
        pt++;
        if (pt>n/2) pt -= n/2;
    }

    return calc(n);
}

int main(){
    int n;
    scanf("%d", &n);
    scanf("%s", a+1);
    n *= 2;

    int cb = 0, cw = 0;
    for (int i=1;i<=n;i++){
        if (a[i]=='B') B[++cb] = i;
        else W[++cw] = i;
    }

    ll ans = 0;

    if (n<=4000){
        for (int z=1;z<=n/2;z++){
            ans = max(ans, calc2(n, z));
        }
    }

    else{
        int l = 1, r = n/2;
        while(r-l>=4){
            int m1 = (l*2+r)/3, m2 = (l+r*2)/3;
            if (calc2(n, m1)<calc2(n, m2)) l = m1+1;
            else r = m2-1;
        }

        for (int z=l;z<=r;z++) ans = max(ans, calc2(n, z));
    }

    printf("%lld\n", ans);
    return 0;
}

Compilation message (stderr)

monochrome.cpp: In function 'int main()':
monochrome.cpp:61:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   61 |     scanf("%d", &n);
      |     ~~~~~^~~~~~~~~~
monochrome.cpp:62:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   62 |     scanf("%s", a+1);
      |     ~~~~~^~~~~~~~~~~

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