【uva】225 - Golygons（dfs有坑）

dfs的路径问题，毕竟坑的是一条路线不能走相同的转弯点，一开始BFS做的存状态超时，之后回溯dfs过的。

感觉没什么难度。

 
这个是TEL的BFS代码：

13970312225GolygonsTime limit exceededC++3.0002014-07-31 09:42:55

#include <vector>#include <list>#include <map>#include <string>#include <set>#include <cstring>#include <deque>#include <queue>#include <stack>#include <bitset>#include <algorithm>#include <functional>#include <numeric>#include <utility>#include <sstream>#include <iostream>#include <iomanip>#include <cstdio>#include <cmath>#include <cstdlib>#include <ctime>using namespace std;typedef long long LL;typedef unsigned long long ULL;#define MAXD 1000#define LEN  300int n;int Map[MAXD][MAXD] = {0};int dir[4][2] = {{1,0},{-1,0},{0,1},{0,-1}}; /*向右走，向左走，向上走，向下走*/int dir_[2][2][2] = {{{0,1},{0,-1}},{{1,0},{-1,0}}};char const _dir[] = "ewns";/*0 1 2 3 分别代表向上，向下，向右，向左*/struct State{    vector<int>rote;  /*路线*/    int now_dir;      /*当前方向*/    int step;         /*当前要走第几步*/    int x,y;          /*当前位置*/};bool can_move(int from_x,int from_y,int to_x,int to_y){    /*判断能否从(from_x,from_y) 走到 (to_x,to_y) */    if(from_x == to_x){        int t1 = min(from_y,to_y);        int t2 = max(from_y,to_y);        for(int i = t1 ; i <= t2 ; i++){            if(Map[to_x][i])                return false;        }    }    else if(from_y == to_y){        int t1 = min(from_x,to_x);        int t2 = max(from_x,to_x);        for(int i = t1 ; i <= t2 ; i++){            if(Map[i][to_y])                return false;        }    }    return true;}void bfs(){    queue<State>q;    for(int i = 0 ; i < 4 ; i++){  /*起始点*/        int _x = LEN + dir[i][0];        int _y = LEN + dir[i][1];        if(!Map[_x][_y]){ /*不是障碍*/            State start;            start.rote.push_back(i);            start.step = 2;            start.now_dir = i;            start.x = _x;            start.y = _y;            q.push(start);        }    }    int cnt = 0;    while(!q.empty()){        State s = q.front(); q.pop();        if(s.step == n + 1){            cnt ++;            for(int i = 0 ; i < s.rote.size(); i++)                printf("%c",_dir[s.rote[i]]);            printf("\n");            continue;        }        int k;        int step = s.step;        if(s.now_dir == 0 || s.now_dir == 1)            k = 0;        else            k = 1;        for(int i = 0; i < 2 ; i++){ /*每次只能转90度的弯*/             int _x = s.x + step * dir_[k][i][0];             int _y = s.y + step * dir_[k][i][1];             if(can_move(s.x,s.y,_x,_y)){                 State temp = s;                 temp.x = _x; temp.y = _y;                 temp.step = step + 1;                 if(k == 0){    /*这一步它向东走*/                    if(i == 0){                    temp.rote.push_back(2);                    temp.now_dir = 2;                    }                    else                    if(i == 1) { /*这一步它向西走*/                    temp.rote.push_back(3);                    temp.now_dir = 3;                    }                 }                 else if(k == 1){                    if(i == 0){  /*这一步它向南走*/                    temp.rote.push_back(0);                    temp.now_dir = 0;                    }                    else                    if(i == 1){  /*这一步它向北走*/                    temp.rote.push_back(1);                    temp.now_dir = 1;                    }                 }                 if(step == n &&(_x != LEN ||_y != LEN)) continue;                 else                 q.push(temp);             }        }    }    printf("Found %d golygon(s).\n",cnt);}int main(){    int T;    scanf("%d",&T);    while(T--){        int m;        scanf("%d%d",&n,&m);        memset(Map,0,sizeof(Map));        for(int i = 0 ; i < m ; i++){            int x , y;            scanf("%d%d",&x,&y);            Map[LEN + x][LEN + y] = 1;        }        bfs();        printf("\n");    }    return 0;}

这个是AC的DFS代码，可以看出来，不同情况下使用DFS和BFS的计算时间差的很大~

13970729225GolygonsAcceptedC++2.2392014-07-31 10:49:47

#include <vector>#include <list>#include <map>#include <string>#include <set>#include <cstring>#include <deque>#include <queue>#include <stack>#include <bitset>#include <algorithm>#include <functional>#include <numeric>#include <utility>#include <sstream>#include <iostream>#include <iomanip>#include <cstdio>#include <cmath>#include <cstdlib>#include <ctime>using namespace std;typedef long long LL;typedef unsigned long long ULL;#define MAXD 1000#define LEN  500int n,cnt;int Map[MAXD][MAXD];int dir[4][2] = {{1,0},{-1,0},{0,1},{0,-1}}; /*向右走，向左走，向上走，向下走*/int dir_[2][2][2] = {{{0,1},{0,-1}},{{1,0},{-1,0}}};char const _dir[] = "ewns";int _vis[50] = {0};/*0 1 2 3 分别代表向上，向下，向右，向左*/int rote[MAXD];  /*路线*/int vis[MAXD][MAXD];struct Dir{    char str[MAXD];    friend bool operator < (Dir p,Dir q){        if(strcmp(p.str,q.str) < 0)            return true;        else            return false;    }}ans[200L];void biao(){    _vis[1] = 1;    _vis[2] = 1;    _vis[3] = 1;    _vis[4] = 1;    _vis[5] = 1;    _vis[6] = 1;    _vis[9] = 1;    _vis[10] = 1;    _vis[11] = 1;   _vis[12] = 1;   _vis[13] = 1;   _vis[14] = 1;    _vis[17] = 1;   _vis[18] = 1;   _vis[19] = 1;   _vis[20] = 1;}bool can_move(int from_x,int from_y,int to_x,int to_y){    /*判断能否从(from_x,from_y) 走到 (to_x,to_y) */    if(from_x == to_x){        int t1 = min(from_y,to_y);        int t2 = max(from_y,to_y);        for(int i = t1 ; i <= t2 ; i++){            if(Map[to_x][i])                return false;        }    }    else if(from_y == to_y){        int t1 = min(from_x,to_x);        int t2 = max(from_x,to_x);        for(int i = t1 ; i <= t2 ; i++){            if(Map[i][to_y])                return false;        }    }    return true;}void dfs(int step,int dir,int x,int y){ /*当前步数，当前方向，当前位置*/     vis[x][y] = 1;     if(step == n && x == LEN && y == LEN){        for(int i = 0 ; i < step ; i++)            ans[cnt].str[i] = _dir[rote[i]];        ans[cnt].str[step] = '\0';        cnt ++;        return ;    }    else if(step == n)        return ;    int k;    if(dir == 0 || dir == 1)        k = 0;    else        k = 1;    for(int i = 0; i < 2 ; i++){ /*每次只能转90度的弯*/         int _x = x + (step + 1) * dir_[k][i][0];         int _y = y + (step + 1) * dir_[k][i][1];         if(!vis[_x][_y] && can_move(x,y,_x,_y)){             if(k == 0){    /*这一步它向东走*/                if(i == 0){                rote[step] = 2;                dfs(step + 1,2,_x,_y);                }                else                if(i == 1) { /*这一步它向西走*/                rote[step] = 3;                dfs(step + 1,3,_x,_y);                }             }             else if(k == 1){                if(i == 0){  /*这一步它向南走*/                rote[step] = 0;                dfs(step + 1,0,_x,_y);                }                else                if(i == 1){  /*这一步它向北走*/                rote[step] = 1;                dfs(step + 1,1,_x,_y);                }             }             vis[_x][_y] = 0;         }     }     return ;}int main(){    int T;    scanf("%d",&T);    biao();    while(T--){        int m;        cnt = 0;        scanf("%d%d",&n,&m);        memset(Map,0,sizeof(Map));        for(int i = 0 ; i < m ; i++){            int x , y;            scanf("%d%d",&x,&y);            Map[LEN + x][LEN + y] = 1;        }        if(!_vis[n]){        for(int i = 0 ; i < 4 ; i++){            int x = LEN + 1 * dir[i][0];            int y = LEN + 1 * dir[i][1];            memset(vis,0,sizeof(vis));            rote[0] = i;            dfs(1,i,x,y);        }        sort(ans,ans + cnt);        for(int i = 0 ; i < cnt ; i++)        printf("%s\n",ans[i].str);        }        printf("Found %d golygon(s).\n",cnt);        printf("\n");    }    return 0;}