POJ 3083 Children of the Candy Corn（DFS + BFS）

题意：

求从进入点到出口，分别按靠左边，右边和最短距离到达出口所学要的步数。

思路：

坐标问题弄的稀里糊涂的，引用 discuss 里面的思路吧：

向左：依左上右下的顺序针方向走。根据上一个来的方向判断当前坐标开始走的方向，按顺时针走即可，回溯时经过的格子数也要增加，并且方向要反向



向右：依右上左下的逆时针方向走即可



最短是普通的 BFS  

 

#include <iostream>

#include <algorithm>

#include <deque>

using namespace std;



const int MAXN = 50;



struct ST {

    int x, y, step;

    ST(int _x, int _y, int _s) : x(_x), y(_y), step(_s) {}

};



char grid[MAXN][MAXN];

bool vis[MAXN][MAXN];

int dir[4][2] = {{0,-1}, {-1,0}, {0,1}, {1,0}};

int ans;



bool lhsDfs(int x, int y, int o, int step) {

    if (grid[x][y] == 'E') {

        ans = step; 

        return true;

    }



    for (int i = o; i < o + 4; ++i) {

        int newx = x + dir[i%4][0];

        int newy = y + dir[i%4][1];



        if (grid[newx][newy] != '#') {

            if (lhsDfs(newx, newy, (i-1+4)%4, step+1))

                return true;

        }

    }

    return false;

}



bool rhsDfs(int x, int y, int o, int step) {

    if (grid[x][y] == 'E') {

        ans = step; 

        return true;

    }



    for (int i = o + 4; i > o; --i) {

        int newx = x + dir[i%4][0];

        int newy = y + dir[i%4][1];



        if (grid[newx][newy] != '#') {

            if (rhsDfs(newx, newy, (i+1)%4, step+1))

                return true;

        }

    }

    return false;

}



int bfs(int x, int y) {

    deque<ST> q;

    q.push_back(ST(x, y, 1));

    vis[x][y] = true;



    while (!q.empty()) {

        ST s = q.front();

        q.pop_front();



        if (grid[s.x][s.y] == 'E') 

            return s.step;



        for (int i = 0; i < 4; ++i) {

            int newx = s.x + dir[i][0];

            int newy = s.y + dir[i][1];



            if (grid[newx][newy] != '#' && !vis[newx][newy]) {

                vis[newx][newy] = true;

                q.push_back(ST(newx, newy, s.step + 1));   

            }

        }

    }

}



int main()

{

    int cases;

    scanf("%d", &cases);



    while (cases--) {

        int row, col;

        scanf("%d %d", &col, &row);



        memset(grid, '#', sizeof(grid));

        for (int i = 1; i <= row; ++i)

            scanf("%s", &grid[i][1]);



        int x, y;

        for (int i = 1; i <= row; ++i) 

            for (int j = 1; j <= col; ++j)

                if (grid[i][j] == 'S') x = i, y = j;



        lhsDfs(x, y, 0, 1);

        printf("%d ", ans);



        rhsDfs(x, y, 0, 1);

        printf("%d ", ans);



        memset(vis, false, sizeof(vis));

        printf("%d\n", bfs(x, y));

    }

    return 0;

}