POJ3669.cpp

#include <iostream>
#include <algorithm>
#include <utility>
#include <map>
#include <queue>
#include <string>
#include <vector>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <ctime>
#include <cmath>

using namespace std;

#define FOR(i, j, k) for(int i = j; i < k; ++i)
#define rep(i, j) FOR(i, 0, j)
#define INF (1 << 30)
#define fi first
#define se second

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef pair<P, int> Pi;
typedef pair<P, P> PP;

const int MOD = 1e9 + 7;
const int dy[]={0, 0, 1, -1};
const int dx[]={1, -1, 0, 0};

template <class T> void chmin(T& a, const T& b) { a = min(a, b); }
template <class T> void chmax(T& a, const T& b) { a = max(a, b); }

int field[400][400];
bool went[400][400];

int bfs(int n) {
    queue<Pi> que;
    que.push(Pi(P(0, 0), n));

    while(!que.empty()) {
        Pi p = que.front(); que.pop();
        if(field[p.fi.se][p.fi.fi] == INF) return p.se;
        if(went[p.fi.se][p.fi.fi]) continue;
        went[p.fi.se][p.fi.fi] = true;
        rep(i, 4) {
            int nx = p.fi.fi + dx[i], ny = p.fi.se + dy[i];
            if(nx < 0 || ny < 0) continue;
            if(field[ny][nx] <= p.se + 1) continue;
            que.push(Pi(P(nx, ny), p.se + 1));
        }
    }
    return INF;
}

signed main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int m;
    scanf("%d", &m);
    rep(i, 400) rep(j, 400) field[i][j] = INF;
    rep(i, m) {
        int x, y, t;
        scanf("%d %d %d", &x, &y, &t);
        chmin(field[y][x], t);
        rep(j, 4) {
            int hx = x + dx[j], hy = y + dy[j];
            if(hx < 0 || hy < 0) continue;
            chmin(field[hy][hx], t);
        }
    }
    int res = bfs(0);
    printf("%d\n", (res == INF) ? -1 : res);
    return 0;
}