Yandex.Algorithm 2018, final round

思路:如果n这个位置加1的话,不同的数的个数要么不变,要么加1,反之,如果不同的数的个数减少,肯定不是n这个位置加1

我们random_shuffle()50次,每次把不是n的位置标记一下,这样有很大的概率把所有的不是n的位置都标记了

代码:

#pragma GCC optimize(2)

#pragma GCC optimize(3)

#pragma GCC optimize(4)

#include<bits/stdc++.h>

using namespace std;

#define fi first

#define se second

#define pi acos(-1.0)

#define LL long long

//#define mp make_pair

#define pb push_back

#define ls rt<<1, l, m

#define rs rt<<1|1, m+1, r

#define ULL unsigned LL

#define pll pair<LL, LL>

#define pli pair<LL, int>

#define pii pair<int, int>

#define piii pair<pii, int>

#define mem(a, b) memset(a, b, sizeof(a))

#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);

#define fopen freopen("in.txt", "r", stdin);freopen("out.txt", "w", stout);

//head

const int N = 1e3 + ;

int a[N];

bool vis[N];

int main() {

    int n, tot = ;

    scanf("%d", &n);

    for (int i = ; i <= n; i++) a[i] = i;

    int pre = n, now;

    while(tot--) {

        random_shuffle(a+, a++n);

        for (int i = ; i <= n; i++) {

            printf("0 %d\n", a[i]);

            fflush(stdout);

            scanf("%d", &now);

            if(now < pre) {

                vis[a[i]] = true;

            }

            pre = now;

        }

    }

    for (int i = ; i <= n; i++) if(!vis[i]) return *printf("1 %d\n", i);

    return ;

}

F Lazy Hash Table

思路:FFT

求最小的m使得任意两个数之间的差值都不是这个m的倍数

用FFT求任意两个数之间的差值

代码:

#pragma GCC optimize(2)

#pragma GCC optimize(3)

#pragma GCC optimize(4)

#include<bits/stdc++.h>

using namespace std;

#define fi first

#define se second

#define pi acos(-1.0)

#define LL long long

//#define mp make_pair

#define pb push_back

#define ls rt<<1, l, m

#define rs rt<<1|1, m+1, r

#define ULL unsigned LL

#define pll pair<LL, LL>

#define pli pair<LL, int>

#define pii pair<int, int>

#define piii pair<pii, int>

#define mem(a, b) memset(a, b, sizeof(a))

#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);

#define fopen freopen("in.txt", "r", stdin);freopen("out.txt", "w", stout);

//head

const int N = 8e6 + , M = 2e6 + ;

int R[N], a[M], b[M];

struct Complex {

    double x, y;

    Complex(double _x=, double _y=) : x(_x),y(_y) {};

    Complex operator + (Complex &t) {return Complex(x+t.x, y+t.y);}

    Complex operator - (Complex &t) {return Complex(x-t.x, y-t.y);}

    Complex operator * (Complex &t) {return Complex(x*t.x - y*t.y, x*t.y + y*t.x);}

}A[N], B[N];

void fft(Complex *x, int n, int type) {

    for (int i = ; i < n; i++) if(i < R[i]) swap(x[i], x[R[i]]);

    for (int i = ; i < n; i<<=) {

        Complex wn(cos(pi/i), type*sin(pi/i));

        for (int j = ; j < n; j+=i<<) {

            Complex w(, );

            for (int k = ; k < i; k++, w=w*wn) {

                Complex X = x[j+k];

                Complex Y = w*x[j+k+i];

                x[j+k] = X + Y;

                x[j+k+i] = X - Y;

            }

        }

    }

}

int main() {

    int n, m = ;

    scanf("%d", &n);

    for (int i = ; i <= n; i++) {

        scanf("%d", &a[i]);

        m = max(m, a[i]);

        A[a[i]] = {, };

    }

    for (int i = ; i <= n; i++) {

        B[m-a[i]] = {, };

    }

    int l = , L = ;

    for (l = ; l < *m+; l <<= ) L++;

    for (int i = ; i < l; i++) {

        R[i] = (R[i>>]>>)|((i&)<<L-);

    }

    fft(A, l, );

    fft(B, l, );

    for (int i = ; i < l; i++) A[i] = A[i] * B[i];

    fft(A, l, -);

    for (int i = ; i <= m; i++) b[i] = (int)(A[i+m].x/l + 0.5);

    for (int i = ; i <= m; i++) {

        bool f = true;

        for (int j = i; j <= m; j += i) {

            if(b[j]) {

                f = false;

                break;

            }

        }

        if(f) {

            printf("%d\n", i);

            exit();

        }

    }

    return ;

}

巴特西

Yandex.Algorithm 2018, final round

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