POJ_1753

Poj 1753 flip game

无需储存每一步的用时，只需储存到每一个状态的最短用时（记忆化搜索)?。 

#include <stdio.h>#include <stdlib.h>#include <string.h>#include <iostream>#include <algorithm>#include <queue>using namespace std;#define MAXN 17#define SIZE 16#define MAXLEN 1<<17#define MIN(a, b) (a < b? a : b)#define INF 0x7fffffffconst int go[] = { 0xc800, 0xe400, 0x7200, 0x3100, 0x8c80, 0x4e40, 0x2720, 0x1310, 0x08c8, 0x04e4, 0x0272, 0x0131, 0x008c, 0x004e, 0x0027, 0x0013}, len = 16;int time[MAXLEN];  // save the mini time to "NUM";char maps[MAXN];int ans;int abs(int k){    return k >= 0 ? k : -k;}class node{public:    int num;    bool flags[SIZE];    node()    {        memset(flags, 0, sizeof(flags));    }    node(const int& k):num(k)    {        memset(flags, 0, sizeof(flags));    }    node(const node &k)    {        this->num = k.num;        for(register int i = 0; i < MAXN; ++i)            this->flags[i] = k.flags[i];    }    void kick(const node &father, const int &k, const int &c)    {        this->num =  (father.num ^ k);        for(register int i = 0; i < SIZE; ++i)            this->flags[i] = father.flags[i];        this->flags[c] = true;    }    bool operator == (const node &k)    {        return this->num == k.num;    }};queue<node> que;node start;void bfs(){    node a, b;    while(!que.empty())        que.pop();    time[start.num] = 0;    que.push(start);    while(!que.empty())    {        a = que.front();        que.pop();        if(a.num == 0 ||a.num == 0xffff)        {            return;        }        for(register int i = 0; i < len; ++i)        {            if(!a.flags[i])            {                b.kick(a, go[i], i);                if(time[b.num] < 0 || (time[b.num] > time[a.num] + 1))  //若未到达过或有更短时间到达该状态则入队列                {                    time[b.num] = time[a.num] + 1;                    que.push(b);                }            }        }    }}void igets(char *s){    char *p = s;    for(int i = 0; i < 4; ++i)    {        for(int j = 0; j < 4; ++j)            *p++ = getchar();        getchar();    }    *p = 0;}void solve(){    igets(maps);    memset(time, -1, sizeof(time));    ans = -1;    start.num = 0;    for(register int i = 0; i < SIZE; ++i)    {        start.num <<= 1;        start.num += (maps[i] == 'w' ? 1 : 0);    }    bfs();    if(time[0] < 0)        time[0] = INF;    if(time[0xffff] < 0)        time[0xffff] = INF;    ans = MIN(time[0], time[0xffff]);    if(ans >= 0 && ans < INF)        printf("%d\n", ans);    else        puts("Impossible");}int main(){    solve();    return 0;}