Submission #3081487

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

#define NDEBUG
#ifdef DEBUG
#include "../cout11.h"
#undef NDEBUG
#endif
#include <cassert>

typedef long long ll;
typedef long double Double;
typedef unsigned long long ull;
typedef pair<int,int> ii;
typedef pair<ll,ll> llll;
typedef pair<double,double> dd;

typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<ii> vii;
typedef vector<vector<ii>> vvii;
typedef vector<ll> vll;
typedef vector<string> vs;
typedef vector<double> vd;
typedef vector<long double> vD;

#define sz(a)  int((a).size())
#define pb  push_back
#define FOR(var,from,to) for(int var=(from);var<=(to);++var)
#define rep(var,n)  for(int var=0;var<(n);++var)
#define rep1(var,n)  for(int var=1;var<=(n);++var)
#define repC2(vari,varj,n)  for(int vari=0;vari<(n)-1;++vari)for(int varj=vari+1;varj<(n);++varj)
#define ALL(c)  (c).begin(),(c).end()
#define RALL(c)  (c).rbegin(),(c).rend()
#define tr(i,c)  for(auto i=(c).begin(); i!=(c).end(); ++i)
#define found(s,e)  ((s).find(e)!=(s).end())
#define mset(arr,val)  memset(arr,val,sizeof(arr))
#define mid(x,y) ((x)+((y)-(x))/2)
#define IN(x,a,b) ((a)<=(x)&&(x)<=(b))
#define cons make_pair


ll gcd(ll a, ll b) { while(a) swap(a, b%=a); return b; }

const ll MOD=1000000007LL;

ll ADD(ll x, ll y) { return (x+y) % MOD; }
ll SUB(ll x, ll y) { return (x-y+MOD) % MOD; }
ll MUL(ll x, ll y) { return x*y % MOD; }
ll POW(ll x, ll e) { ll v=1; for(; e; x=MUL(x,x), e>>=1) if (e&1) v = MUL(v,x); return v; }
ll DIV(ll x, ll y) { /*assert(y%MOD!=0);*/ return MUL(x, POW(y, MOD-2)); }
// ll comb(ll n, ll k) { ll v=1; for(ll i=1; i<=k; i++) v = DIV(MUL(v, n-i+1),i); return v; }
//

#define INTSPACE 12
char _buf[INTSPACE*1000000 + 3];

int loadint() {
    if (fgets(_buf, INTSPACE+3, stdin)==NULL) return 0;
    return atoi(_buf);
}

int loadvec(vector<int>& v, int N=-1) {
    if (N == -1) {
        N = loadint();
        if (N==0) return 0;
    }
    int bufsize = INTSPACE*N + 3;
    if (fgets(_buf, bufsize, stdin)==NULL) return 0;
    v.resize(N);

    int i=0;
    bool last = false;
    for (char *p=&_buf[0]; ;) {
        char *q = p;
        while (*q > ' ') ++q;
        if (*q == 0x0D || *q == 0x0A) last = true;
        *q = 0;
        v[i++] = atoi(p);
        if (last || i == N) break;
        p = q+1;
    }
    // assert(i <= N);
    return i;
}
void read_cr() {
    fgets(_buf, 256, stdin);
}


// Fenwick Tree (Binary Indexed Tree, BIT)
template <typename T, int base=0>
class fenwick_tree_0 { // 0-base
 public:
    vector<T> x;
 public:
    fenwick_tree_0(int n) : x(n+base,0) { }
    void add(int k, T a=1) { for (; k<x.size(); k|=k+1) x[k] += a; }
    T sum(int i, int j) { // [i,j]
        if (i == base) {
            T S = 0; for (; j>=0; j=(j&(j+1))-1) S += x[j]; return S;
        } else {
            return sum(base, j) - sum(base, i-1);
        }
    }
};

template <typename T, int base=1>
class fenwick_tree_1 { // 1-base
 public:
    vector<T> x;
 public:
    fenwick_tree_1(int n) : x(n+base,0) { }
    void add(int k, T a=1) { for (; k<=x.size(); k+=k&-k) x[k] += a; }
    T sum(int i, int j) { // [i,j]
        if (i == base) {
            T S = 0; for (; j>0; j-=j&-j) S += x[j]; return S;
        } else {
            return sum(base, j) - sum(base, i-1);
        }
    }
};


int zaatsu(int N, vi& src, vi &dest, int offset=0) {
    set<int> uniq(ALL(src));
    map<int,int> mp;
    int ix = 0;
    for (int x : uniq) mp[x] = ix++;

    dest.resize(N);
    for (int i=0; i<N; ++i) {
        dest[i] = offset + mp[src[i]];
    }
    return ix; // num_indices
}

ll count_inversion(vector<int>& a) {
    int N=a.size();
    vi b(N);
    int num_indices = zaatsu(N, a, b, 1);
    // cerr << a << num_indices << b << endl;

    int _N = 1; while (_N < N+1) _N *= 2;
    fenwick_tree_0<int> ft(_N);

    ll cnt = 0;
    for (int i=N-1; i>=0; --i) {
        cnt += ft.sum(1, b[i]-1);
        ft.add(b[i]);
    }
    return cnt;
}

int N;
vector<int> a;
// vector<int> b, s;
vector<int> s;

bool f(int x){
    ll M = (ll)(N+1) * N / 2; // N+1 C 2

    // rep(i,N) b[i] = (a[i] >= x) ? 1 : -1;
    // s[0] = 0; rep(i,N) s[i+1] = s[i] + b[i];
    s[0] = 0; rep(i,N) s[i+1] = s[i] + ( (a[i] >= x) ? 1 : -1 );

    ll inv = count_inversion(s);

    ll good = M - inv;
#ifdef DEBUG
    fprintf(stderr, "f(%d): M=%lld N=%d, inv=%lld ; %lld >= %lld ?\n", x, M,N,inv, good, (M+1)/2);
#endif
    return good >= (M+1)/2;
}


int solve() {
    // b.resize(N);
    s.resize(N+1);

    int lo = INT_MAX, hi = INT_MIN;
    rep(i,N) {
        lo = min(lo, a[i]); // true side
        hi = max(hi, a[i]); // false side
    }

    --lo;
    ++hi;
    // assert(f(lo) == true);
    // assert(f(hi) == false);


    while (lo+1 < hi) {
        int mi = (lo + hi)/2;
#ifdef DEBUG
        fprintf(stderr, "[%d %d %d)...\n", lo,mi,hi);
#endif
        if (f(mi)) {
            lo = mi;
        } else {
            hi = mi;
        }
    }
    return lo;
}

int main() {
    N = loadint();
    loadvec(a, N);
    cout << solve() << endl;
    return 0;
}

Submission Info

Submission Time
Task D - Median of Medians
User naoya_t
Language C++14 (GCC 5.4.1)
Score 700
Code Size 5254 Byte
Status
Exec Time 557 ms
Memory 11904 KB

Compile Error

./Main.cpp: In function ‘void read_cr()’:
./Main.cpp:87:28: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result]
     fgets(_buf, 256, stdin);
                            ^

Test Cases

Set Name Score / Max Score Test Cases
Sample 0 / 0 0_00.txt, 0_01.txt, 0_02.txt
All 700 / 700 0_00.txt, 0_01.txt, 0_02.txt, 1_00.txt, 1_01.txt, 1_02.txt, 1_03.txt, 1_04.txt, 1_05.txt, 1_06.txt, 1_07.txt, 1_08.txt, 1_09.txt, 1_10.txt, 1_11.txt, 1_12.txt, 1_13.txt, 1_14.txt, 1_15.txt
Case Name Status Exec Time Memory
0_00.txt 1 ms 256 KB
0_01.txt 1 ms 256 KB
0_02.txt 1 ms 256 KB
1_00.txt 1 ms 256 KB
1_01.txt 1 ms 256 KB
1_02.txt 45 ms 11008 KB
1_03.txt 50 ms 11904 KB
1_04.txt 557 ms 9000 KB
1_05.txt 476 ms 9000 KB
1_06.txt 421 ms 6696 KB
1_07.txt 363 ms 6696 KB
1_08.txt 263 ms 6904 KB
1_09.txt 287 ms 7032 KB
1_10.txt 269 ms 6908 KB
1_11.txt 281 ms 6908 KB
1_12.txt 271 ms 6784 KB
1_13.txt 289 ms 7028 KB
1_14.txt 269 ms 6904 KB
1_15.txt 272 ms 7028 KB