SGU 237 Galaxy X: Episode I - Masters of Mind(最短回文串)
题目链接：http://acm.sgu.ru/problem.php?contest=0&problem=237
题意：给出一个串。星号可以被任意替换（包括空串），问号必须且只能被一个字母替换，感叹号必须且只能被三个字符替换。求替换后的最短回文串？最短的情况下字典序最小？
思路：f[i][j]表示i到j形成回文串的最小。长度从小到大枚举即可。
#include <iostream>
#include <cstdio>
#include <string.h>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <map>
#define max(x,y) ((x)>(y)?(x):(y))
#define min(x,y) ((x)<(y)?(x):(y))
#define abs(x) ((x)>=0?(x):-(x))
#define i64 long long
#define u32 unsigned int
#define u64 unsigned long long
#define clr(x,y) memset(x,y,sizeof(x))
#define CLR(x) x.clear()
#define ph(x) push(x)
#define pb(x) push_back(x)
#define Len(x) x.length()
#define SZ(x) x.size()
#define PI acos(-1.0)
#define sqr(x) ((x)*(x))
#define MP(x,y) make_pair(x,y)
#define FOR0(i,x) for(i=0;i<x;i++)
#define FOR1(i,x) for(i=1;i<=x;i++)
#define FOR(i,a,b) for(i=a;i<=b;i++)
#define DOW0(i,x) for(i=x;i>=0;i--)
#define DOW1(i,x) for(i=x;i>=1;i--)
#define DOW(i,a,b) for(i=a;i>=b;i--)
using namespace std;
void RD(int &x){scanf("%d",&x);}
void RD(i64 &x){scanf("%I64d",&x);}
void RD(u32 &x){scanf("%u",&x);}
void RD(double &x){scanf("%lf",&x);}
void RD(int &x,int &y){scanf("%d%d",&x,&y);}
void RD(i64 &x,i64 &y){scanf("%I64d%I64d",&x,&y);}
void RD(u32 &x,u32 &y){scanf("%u%u",&x,&y);}
void RD(double &x,double &y){scanf("%lf%lf",&x,&y);}
void RD(int &x,int &y,int &z){scanf("%d%d%d",&x,&y,&z);}
void RD(i64 &x,i64 &y,i64 &z){scanf("%I64d%I64d%I64d",&x,&y,&z);}
void RD(u32 &x,u32 &y,u32 &z){scanf("%u%u%u",&x,&y,&z);}
void RD(double &x,double &y,double &z){scanf("%lf%lf%lf",&x,&y,&z);}
void RD(char &x){x=getchar();}
void RD(char *s){scanf("%s",s);}
void RD(string &s){cin>>s;}
void PR(int x) {printf("%d\n",x);}
void PR(i64 x) {printf("%I64d\n",x);}
void PR(u32 x) {printf("%u\n",x);}
void PR(u64 x) {printf("%llu\n",x);}
void PR(double x) {printf("%.4lf\n",x);}
void PR(char x) {printf("%c\n",x);}
void PR(char *x) {printf("%s\n",x);}
void PR(string x) {cout<<x<<endl;}
const int N=800;
char a[N],b[N],g[3][N][N];
int f[3][N],n;
int i,j,k,p0,p1,p2;
char c1,c2;
void assign(char *s,int L)
{
f[p2][i]=L;
strcpy(g[p2][i],s);
}
void update(char *s,int L)
{
if(f[p2][i]>L||f[p2][i]==L&&strcmp(g[p2][i],s)>0)
{
assign(s,L);
}
}
int main()
{
gets(b);
for(i=0;b[i];i++)
{
if(b[i]=='!') a[n++]='?',a[n++]='?',a[n++]='?';
else a[n++]=b[i];
}
for(i=0;i<n;i++)
{
if(a[i]=='*') f[1][i]=0;
else
{
f[1][i]=1;
if(a[i]=='?') g[1][i][0]='a';
else g[1][i][0]=a[i];
}
}
p0=0;p1=1;p2=2;
for(j=1;j<n;j++)
{
for(i=0;i+j<n;i++)
{
c1=a[i];
c2=a[i+j];
if(c1=='*')
{
if(c2=='*')
{
assign(g[p0][i+1],f[p0][i+1]);
update(g[p1][i],f[p1][i]);
update(g[p1][i+1],f[p1][i+1]);
}
else
{
assign(g[p1][i+1],f[p1][i+1]);
if(c2=='?') c2='a';
strcpy(b+1,g[p1][i]);
k=f[p1][i];
b[0]=b[k+1]=c2;
b[k+2]=0;
k+=2;
update(b,k);
}
}
else if(c2=='*')
{
assign(g[p1][i],f[p1][i]);
if(c1=='?') c1='a';
strcpy(b+1,g[p1][i+1]);
k=f[p1][i+1];
b[0]=b[k+1]=c1;
b[k+2]=0;
k+=2;
update(b,k);
}
else
{
if(f[p0][i+1]>=800||c1!=c2&&c1!='?'&&c2!='?')
{
assign("",800);
}
else
{
if(c1=='?')
{
if(c2=='?') c1='a';
else c1=c2;
}
strcpy(g[p2][i]+1,g[p0][i+1]);
k=f[p0][i+1];
g[p2][i][0]=g[p2][i][k+1]=c1;
g[p2][i][k+2]=0;
f[p2][i]=k+2;
}
}
}
p0=p1;
p1=p2;
p2=3^p0^p1;
}
if(f[p1][0]<800)
{
puts("YES");
puts(g[p1][0]);
}
else
{
puts("NO");
}
return 0;
}