hdu 1044 Collect More Jewels

并没有做过这种类型的题目,不太会做...看了一下大神的代码,然后自己敲...额..思路一样了,代码也差不多..

http://www.cnblogs.com/kuangbin/archive/2012/08/14/2637512.html

先通过BFS预处理任意两点之间的距离,然后通过DFS暴力模拟路径,算出最优解.

感觉自己可能对BFS理解比DFS更深一点,或者说,BFS比较简单一点吧...

这题还有一种解法是状态压缩+BFS...通过开设一个int型变量记录是否拿到宝物,然后暴力..不过这种方法一不小心就超时了..需要注意一些优化的细节;

例如: 0000000000 | 0000000001 ,这样就拿到第一个宝箱...解法和HDU 1429 是相似的.

#include <iostream>
#include <string.h>
#include <queue>
#define MAXN 55
int T, H, W, L, M,Sum,ans,Case;
int dir[4][2] = { 0, 1, 0, -1, 1, 0, -1, 0 };
int dis[12][12];
int value[12];
bool visit_bfs[MAXN][MAXN];
bool visit_dfs[MAXN];
char map[MAXN][MAXN];
struct node{
    int x, y;
    int step;
};
using namespace std;
bool check(int x, int y)
{
    if (x<0 || x>=W  || y<0 || y>=H  || map[x][y] == '*')
        return false;
    return true;
}
int bfs(int x,int y,int begin)
{
    node cur, next;
    queue<node> game;
    memset(visit_bfs, false, sizeof(visit_bfs));
    cur.x = x, cur.y = y, cur.step = 0;
    visit_bfs[x][y] = true;
    game.push(cur);
    while (!game.empty())
    {
        cur = game.front();
        game.pop();
        for (int i = 0; i < 4; i++)
        {
            next.x = cur.x + dir[i][0];
            next.y = cur.y + dir[i][1];            
            if (!check(next.x, next.y) || visit_bfs[next.x][next.y])
                continue;
        //    cout << next.x << " " << next.y << endl;
            visit_bfs[next.x][next.y] = true;
            next.step = cur.step + 1;
            if (map[next.x][next.y] == '@'){
                dis[begin][0] = next.step;
            }
            else if (map[next.x][next.y] == '<'){
                dis[begin][M+1] = next.step;
            }
            else if (map[next.x][next.y] >= 'A' && map[next.x][next.y] <= 'Z')
            {
                dis[begin][map[next.x][next.y] - 'A' + 1] = next.step;
            }
            game.push(next);
        }
    }
    return 0;
}
void dfs(int cur,int score,int time)
{
    if (ans == Sum)
        return;
    if (time > L)
        return;
    if (cur > M){
        if (score > ans)
            ans = score;
    }
    for (int i = 0; i <= M+1; i++)
    {
        if (!visit_dfs[i]&&dis[cur][i]){
            visit_dfs[i] = true;
            dfs(i, score + value[i], time + dis[cur][i]);
            visit_dfs[i] = false;
        }
    }
}
int main()
{
    //freopen("test.txt", "r", stdin);
    Case = 1;
    scanf("%d", &T);
    while (T--)
    {
        scanf("%d%d%d%d", &H, &W, &L, &M);
        Sum = 0;
        for (int i = 1; i <= M; i++){
            scanf("%d", value + i);
            Sum += value[i];
        }
        value[0] = value[M+1] = 0;
        memset(visit_dfs, false, sizeof(visit_dfs));
        memset(dis, 0, sizeof(dis));
        for (int i = 0; i < W; i++)
            scanf("%s", map + i);
        for (int i = 0; i < W;i++)
        for (int j = 0; j < H; j++)
        {
            if (map[i][j] == '@')
                bfs(i,j,0);
            else if (map[i][j] == '<')
                bfs(i,j,M+1);
            else if (map[i][j] >= 'A' && map[i][j] <= 'J')
                bfs(i,j,map[i][j]-'A'+1);
        }
        ans = -1;
        dfs(0, 0, 0);    
        if (Case != 1)
            puts("");
        printf("Case %d:
", Case++);    
        if (ans == -1){
            puts("Impossible");
        }
        else{
            printf("The best score is %d.
", ans);
        }
    }
    return 0;
}