Submission #337629

#	Time	Username	Problem	Language	Result	Execution time	Memory
337629		blue	Aliens (IOI07_aliens)	C++11	100 / 100	2 ms	372 KiB

aliens

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

/*
    Searching for x0+1, x0+2, x0+4, x0+8... and the same y=y0, and then performing a binary search, we can find
    the right edge of the flattened square containing x0, in 30+30=60 queries.
    The binary search cannot return a false positive because the flattened squares are separated by non-flattened
    squares.

    Also, the left edge in 60 queries.
    Also, the bottom edge in 60 queries.

    Using the side length and bottom edge, we already know the top edge.

    Using 2 queries for left and right, and 2 queries for top and bottom, we can figure out which flattened
    square we are currently in.

    This information should be sufficient to locate the center.
*/

long long N, X0, Y0; //side of meadow, coordinates of one flattened square.

int query(long long x, long long y)
{
    if(x < 1 || N < x) return 0;
    if(y < 1 || N < y) return 0;

    cout << "examine " << x << ' ' << y << '\n';
    string s;
    cin >> s;
    return (s == "true");
}

void solve(long long x, long long y)
{
    cout << "solution " << x << ' ' << y << '\n';
}

int main()
{

    cin >> N >> X0 >> Y0;

    long long l_edge, r_edge, b_edge, t_edge;

    long long a, b, m;


//-----------------------------------------------
// cout << "part 1\n";

    a = X0;
    for(b = X0+1; b <= N; b += (b - X0))
    {
        if(query(b, Y0)) a = b;
        else break;
    }
    b = min(b-1, N);

    while(a != b)
    {
        m = (a+b)/2+1;
        if(query(m, Y0)) a = m;
        else b = m-1;
    }
    b_edge = a;


//-----------------------------------------------
    // cout << "part 2\n";

    a = Y0;
    for(b = Y0+1; b <= N; b += (b - Y0))
    {
        if(query(X0, b)) a = b;
        else break;
    }
    b = min(b-1, N);

    while(a != b)
    {
        m = (a+b)/2+1;
        if(query(X0, m)) a = m;
        else b = m-1;
    }
    r_edge = a;


//-----------------------------------------------
// cout << "part 3\n";
    b = Y0;
    for(a = Y0-1; a >= 1; a -= (Y0 - a))
    {
        // cout << a << ' ' << query(X0, a) << '\n';
        if(query(X0, a)) b = a;
        else break;
    }
    a = max(a+1, 1LL);
    // cout << a << '\n';

    while(a != b)
    {
        // cout << a << ' ' << b << '\n';
        m = (a+b)/2;
        if(query(X0, m)) b = m;
        else a = m+1;
    }
    // cout << a << '\n';
    l_edge = b;

//-----------------------------------------------

    int s = r_edge - (l_edge - 1);

    // cout << s << '\n';

    t_edge = b_edge - s + 1;
    // cout << t_edge << ' ' << b_edge << ' ' << l_edge << ' ' << r_edge << '\n';



    int cx = (t_edge + b_edge)/2;
    int cy = (l_edge + r_edge)/2;

    int res_x = cx, res_y = cy;

    if(query(cx, cy + 4*s)) res_y = cy + 2*s;
    else if(query(cx, cy + 2*s) && !query(cx, cy - 2*s)) res_y = cy + s;
    else if(query(cx, cy - 4*s)) res_y = cy - 2*s;
    else if(query(cx, cy - 2*s) && !query(cx, cy + 2*s)) res_y = cy - s;

    if(query(cx + 4*s, cy)) res_x = cx + 2*s;
    else if(query(cx + 2*s, cy) && !query(cx - 2*s, cy)) res_x = cx +  s;
    else if(query(cx - 4*s, cy)) res_x = cx -  2*s;
    else if(query(cx - 2*s, cy) && !query(cx + 2*s, cy)) res_x = cx -  s;

    solve(res_x, res_y);
}

• Subtask 1: 10 / 10
• Subtask 2: 10 / 10
• Subtask 3: 10 / 10
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 10 / 10
• Subtask 9: 10 / 10
• Subtask 10: 10 / 10