POJ

题目：在一个4*4的格子里面，x和o两个人玩游戏，x画'x'，o画'o'，x先手，给定x和o都已经画了一定步数的局面，问x是不是必胜的，如果是，输出他应该画在哪个位置

思路：极小极大搜索+alpha-beta剪枝

代码：

#pragma comment(linker, "/STACK:1024000000,1024000000")#include<iostream>#include<algorithm>#include<ctime>#include<cstdio>#include<cmath>#include<cstring>#include<string>#include<vector>#include<map>#include<set>#include<queue>#include<stack>#include<list>#include<numeric>using namespace std;#define LL long long#define ULL unsigned long long#define INF 0x3f3f3f3f#define mm(a,b) memset(a,b,sizeof(a))#define PP puts("*********************");template<class T> T f_abs(T a){ return a > 0 ? a : -a; }template<class T> T gcd(T a, T b){ return b ? gcd(b, a%b) : a; }template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}// 0x3f3f3f3f3f3f3f3f//0x3f3f3f3fchar str[10][10];int chess;int check(int r,int c){    int cnt=0;    for(int i=0;i<4;i++)//同一行        if(str[r][i]=='x') cnt++;        else if(str[r][i]=='o') cnt--;    if(cnt==4||cnt==-4) return 1;    cnt=0;    for(int i=0;i<4;i++)//同一列        if(str[i][c]=='x') cnt++;        else if(str[i][c]=='o') cnt--;    if(cnt==4||cnt==-4) return 1;    cnt=0;    for(int i=0;i<4;i++)//正对角线        if(str[i][i]=='x') cnt++;        else if(str[i][i]=='o') cnt--;    if(cnt==4||cnt==-4) return 1;    cnt=0;    for(int i=0;i<4;i++)//反对角线        if(str[i][3-i]=='x') cnt++;        else if(str[i][3-i]=='o') cnt--;    if(cnt==4||cnt==-4) return 1;    return 0;}int MaxSearch(int x,int y,int alpha);int MinSearch(int x,int y,int beta);int MinSearch(int x,int y,int beta){    int ans=1;    if(check(x,y)) return ans;//x win    if(chess==16) return 0;//x not win    for(int i=0;i<4;i++)        for(int j=0;j<4;j++){            if(str[i][j]!='.')                continue;            str[i][j]='o';            chess++;            int tmp=MaxSearch(i,j,ans);            str[i][j]='.';            chess--;            if(ans>tmp) ans=tmp;            if(ans<=beta) return ans;        }    return ans;}int MaxSearch(int x,int y,int alpha){    int ans=0;    if(check(x,y)) return ans;//o win    if(chess==16) return 0;//x not win    for(int i=0;i<4;i++)        for(int j=0;j<4;j++){            if(str[i][j]!='.')                continue;            str[i][j]='x';            chess++;            int tmp=MinSearch(i,j,ans);            str[i][j]='.';            chess--;            if(ans<tmp) ans=tmp;            if(ans>=alpha) return ans;        }    return ans;}int solve(int &x,int &y){    for(x=0;x<4;x++)        for(y=0;y<4;y++){            if(str[x][y]!='.')                continue;            str[x][y]='x';            chess++;            if(MinSearch(x,y,0)==1)                return 1;            str[x][y]='.';            chess++;        }    return 0;}int main(){//    freopen("D:\\input.txt","r",stdin);//    freopen("D:\\output.txt","w",stdout);    char ch[10];    while(~scanf("%s",ch)){        if(ch[0]=='$')            break;        for(int i=0;i<4;i++)            scanf("%s",str[i]);        chess=0;        for(int i=0;i<4;i++)            for(int j=0;j<4;j++)                if(str[i][j]!='.')                    chess++;        int x,y;        if(solve(x,y)) printf("(%d,%d)\n",x,y);        else printf("#####\n");    }    return 0;}