北大 算法 2.2 递归 小游戏

#include <iostream>#include <stdio.h>using namespace std;#include <memory.h>#define MAXIN 75char board[MAXIN+2][MAXIN+2];int minstep,w,h,to[4][2]={{1,0},{0,1},{-1,0},{0,-1}};bool mark[MAXIN+2][MAXIN+2];void Search(int now_x,int now_y,int end_x,int end_y,int step,int f){    if(step>minstep) return;    if(now_x == end_x && now_y == end_y){        if(minstep>step){            minstep = step;            return;        }    }    for(int i = 0;i<4;i++){        int x = now_x + to[i][0];        int y = now_y + to[i][1];        if( ((x>-1) && (x<w+2) && (y>-1) && (y<h+2))           &&((board[y][x] == ' ' && mark[y][x] == false)||(x == end_x&&y==end_y&&board[y][x]=='X'))){                mark[y][x] = true;                if(f==i) Search(x,y,end_x,end_y,step,i);                else Search(x,y,end_x,end_y,step+1,i);                mark[y][x] = false; //回溯,该位置未曾走过           }    }}int main(){    int Boardnum = 0;    while(scanf("%d %d",&w,&h)){        if(w==0 && h == 0) break;        Boardnum++;        printf("Board #%d:\n",Boardnum);        int i,j;        for(i=0;i<MAXIN+2;i++){            board[0][i] = board[i][0] = ' ';        }        for(i=1;i <= h;i++){            getchar();            for(j=1;j<=w;j++) board[i][j] = getchar();        }        for(i=0;i<=w;i++)            board[h+1][i+1] = ' ';        for(i=0;i<=h;i++)            board[i+1][w+1] = ' ';        int begin_x,begin_y,end_x,end_y,count = 0;        while(scanf("%d %d %d %d",&begin_x,&begin_y,&end_x,&end_y)&&begin_x > 0   ){            count++;            minstep = 100000;            memset(mark,false,sizeof(mark));            Search(begin_x,begin_y,end_x,end_y,0,-1);            if(minstep<100000) printf("Pair %d: %d segments.\n",count,minstep);            else printf("Pair %d: impossible.\n",count);        }        printf("\n");    }    return 0;}