ROBOCON - VOI 2012 Robocon

Tác giả: RR

Ngôn ngữ: C++

#include <sstream>
#include <iomanip>
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <string>
#include <deque>
#include <complex>

#define FOR(i,a,b) for(int i=(a),_b=(b); i<=_b; i++)
#define FORD(i,a,b) for(int i=(a),_b=(b); i>=_b; i--)
#define REP(i,a) for(int i=0,_a=(a); i<_a; i++)
#define FORN(i,a,b) for(int i=(a),_b=(b);i<_b;i++)
#define DOWN(i,a,b) for(int i=a,_b=(b);i>=_b;i--)
#define SET(a,v) memset(a,v,sizeof(a))
#define sqr(x) ((x)*(x))
#define ll long long
#define F first
#define S second
#define PB push_back
#define MP make_pair

#define DEBUG(x) cout << #x << " = "; cout << x << endl;
#define PR(a,n) cout << #a << " = "; FOR(_,1,n) cout << a[_] << ' '; cout << endl;
#define PR0(a,n) cout << #a << " = "; REP(_,n) cout << a[_] << ' '; cout << endl;
using namespace std;

//Buffer reading
int INP,AM,REACHEOF;
#define BUFSIZE (1<<12)
char BUF[BUFSIZE+1], *inp=BUF;
#define GETCHAR(INP) { \
    if(!*inp) { \
        if (REACHEOF) return 0;\
        memset(BUF,0,sizeof BUF);\
        int inpzzz = fread(BUF,1,BUFSIZE,stdin);\
        if (inpzzz != BUFSIZE) REACHEOF = true;\
        inp=BUF; \
    } \
    INP=*inp++; \
}
#define DIG(a) (((a)>='0')&&((a)<='9'))
#define GN(j) { \
    AM=0;\
    GETCHAR(INP); while(!DIG(INP) && INP!='-') GETCHAR(INP);\
    if (INP=='-') {AM=1;GETCHAR(INP);} \
    j=INP-'0'; GETCHAR(INP); \
    while(DIG(INP)){j=10*j+(INP-'0');GETCHAR(INP);} \
    if (AM) j=-j;\
}
//End of buffer reading

const long double PI = acos((long double) -1.0);

int n, a[511][511];
pair<int,int> qu[2][2][511*511];
int top[2][2];
bool mark[2][2][511][511];

const int di[2][3] = {{0,1,1}, {0,1,1}};
const int dj[2][3] = {{1,0,1}, {-1,0,-1}};

bool ok(pair<int,int> v) {
    return v.F > 0 && v.F <= n && v.S > 0 && v.S <= n && a[v.F][v.S] == 0;
}

int main() {
    int k;
    scanf("%d%d", &n, &k);
    while (k--) {
        int u, v; scanf("%d%d", &u, &v);
        a[u][v] = 1;
    }
    if (n == 1) {
        puts("0");
        return 0;
    }
    // queue(turn, robot, id)
    top[0][0] = 1; qu[0][0][1] = MP(1,1);
    top[0][1] = 1; qu[0][1][1] = MP(1,n);
    int cur = 0;

    FOR(time,1,n+n) {
        cur = 1 - cur;
        memset(mark[cur], 0, sizeof mark[cur]);
        REP(robot,2) {
            top[cur][robot] = 0;
            pair<int,int> u, v;

            FOR(i,1,top[1-cur][robot]) {
                u = qu[1-cur][robot][i];
                REP(dir,3) {
                    v = MP(u.F + di[robot][dir], u.S + dj[robot][dir]);
                    if (!ok(v)) continue;
                    if (!mark[cur][robot][v.F][v.S]) {
                        mark[cur][robot][v.F][v.S] = true;
                        qu[cur][robot][++top[cur][robot]] = v;
                    }
                }
            }
        }

        bool ok = false;
        FOR(i,1,top[cur][0]) {
            pair<int,int> u = qu[cur][0][i];
            if (mark[cur][0][u.F][u.S] && mark[cur][1][u.F][u.S]) {
                ok = true;
                break;
            }
        }
        if (ok) {
            printf("%d\n", time);
            return 0;
        }
    }
    return 0;
}

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