【枚举+最短路】HDU 2363 Cycling

http://acm.hdu.edu.cn/showproblem.php?pid=2363

题意：求最小高度差下的最短路

#include <iostream>
#include <fstream>
#include <algorithm>
#include <string>
#include <set>
//#include <map>
#include <queue>
#include <utility>
#include <iomanip>
#include <stack>
#include <list>
#include <vector>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
//#include <ctime>
#include <ctype.h>
using namespace std;
#define LL __int64
#define inf 0x3fffffff
#define M 105

struct xxx{
    int high;
    int low;
}x[10005];

struct son{
    int v;
    int w;
};

vector<son> g[M];
int dist[M], n, H[M];
bool inq[M];

bool cmp (xxx a, xxx b)
{
    return (a.high - a.low) < (b.high - b.low);
}

void spfa (int low, int high)
{
    int i, v, w, u = 1;
    for (i = 1; i <= n; i++)
    {
        dist[i] = inf;
        inq[i] = false;
    }
    queue<int> q;
    q.push (u);
    dist[u] = 0;
    inq[u] = true;
    while (!q.empty())
    {
        u = q.front();
        q.pop();
        inq[u] = false;
        if (H[u] < low || H[u] > high)    //起点也要限制
            continue;
        for (i = 0; i < g[u].size(); i++)
        {
            v = g[u][i].v;
            if (H[v] < low || H[v] > high)    //高度的限制
                continue;
            w = g[u][i].w;
            if (dist[u] + w < dist[v])
            {
                dist[v] = dist[u] + w;
                if (!inq[v])
                {
                    q.push (v);
                    inq[v] = true;
                }
            }
        }
    }
}

int main()
{
    int t, m, u, v, w, i, j, k;
    son s;
    scanf ("%d", &t);
    while (t--)
    {
        scanf ("%d%d", &n, &m);
        for (i = 1; i <= n; i++)
        {
            scanf ("%d", H+i);
            g[i].clear();
        }
        k = 0;
        for (i = 1; i <= n; i++)
        {
            for (j = i; j <= n; j++)    //不能写成j=i+1，想想起点=终点的情况
            {
                x[k].low = min (H[i], H[j]);
                x[k++].high = max (H[i], H[j]);
            }
        }
        while (m--)
        {
            scanf ("%d%d%d", &u, &v, &w);
            s.v = v;
            s.w = w;
            g[u].push_back (s);
            s.v = u;
            g[v].push_back (s);
        }
        sort (x, x+k, cmp);        //按差排序
        for (i = 0; i < k; i++)    //差从小到大暴力枚举
        {
            spfa (x[i].low, x[i].high);
            if (dist[n] != inf)    //一旦可到达，立刻得出答案
                break;
        }
        printf ("%d %d\n", x[i].high-x[i].low, dist[n]);
    }
    return 0;
}

评论

1 楼 panyanyany 2012-01-24  

靠，又不会做……本来想先求最小高度差的，可以求来求去求不了……