BZOJ3916: [Baltic2014]friends

题目:http://www.lydsy.com/JudgeOnline/problem.php?id=3916

题解:随便hash.刚开始看错题WA了N发.(我连双hash都写了!)

代码:

 1 #include<cstdio>
 2 #include<cstdlib>
 3 #include<cmath>
 4 #include<cstring>
 5 #include<algorithm>
 6 #include<iostream>
 7 #include<vector>
 8 #include<map>
 9 #include<set>
10 #include<queue>
11 #include<string>
12 #define inf 1000000000
13 #define maxn 2000000+5
14 #define maxm 200000+5
15 #define eps 1e-6
16 #define ll unsigned int
17 #define pa pair<int,int>
18 #define for0(i,n) for(int i=0;i<=(n);i++)
19 #define for1(i,n) for(int i=1;i<=(n);i++)
20 #define for2(i,x,y) for(int i=(x);i<=(y);i++)
21 #define for3(i,x,y) for(int i=(x);i>=(y);i--)
22 #define for4(i,x) for(int i=head[x],y=e[i].go;i;i=e[i].next,y=e[i].go)
23 #define for5(n,m) for(int i=1;i<=n;i++)for(int j=1;j<=m;j++)
24 #define lch k<<1,l,mid
25 #define rch k<<1|1,mid+1,r
26 #define sqr(x) (x)*(x)
27 #define db double
28 using namespace std;
29 inline int read()
30 {
31     int x=0,f=1;char ch=getchar();
32     while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
33     while(ch>='0'&&ch<='9'){x=10*x+ch-'0';ch=getchar();}
34     return x*f;
35 }
36 int n,pos;
37 char s[maxn];
38 ll h[maxn],p[maxn];
39 inline ll get(int x,int y){return x>y?0:h[y]-h[x-1]*p[y-x+1];}
40 ll ans,t1,t2;
41 inline bool check(int x)
42 {
43    if(x>n>>1)t1=get(1,n>>1),t2=(get((n>>1)+1,x-1)*p[n-x]+get(x+1,n));
44    else t1=get(n-(n>>1)+1,n),t2=(get(1,x-1)*p[(n>>1)-x+1]+get(x+1,(n>>1)+1));
45    return t1==t2;
46 }
47 int main()
48 {
49    freopen("input.txt","r",stdin);
50    freopen("output.txt","w",stdout);
51    n=read();scanf("%s",s+1);
52    if(n%2==0){printf("NOT POSSIBLE\n");return 0;}
53    p[0]=1;
54    for1(i,n)h[i]=h[i-1]*13131+s[i]-'A',p[i]=p[i-1]*13131;
55    for1(i,n)if(check(i))
56    {
57      pos=i;
58      if(!ans)ans=t1;
59      else if(t1!=ans){printf("NOT UNIQUE\n");return 0;};
60    }
61    if(!pos)printf("NOT POSSIBLE\n");
62    else
63    {
64      if(pos>n>>1)for1(i,n>>1)printf("%c",s[i]);
65      else for2(i,n-(n>>1)+1,n)printf("%c",s[i]);
66      printf("\n");
67    }
68    return 0;
69 }
View Code

 字体为什么忽然变了好鬼畜

posted @ 2015-03-31 17:55 ZYF-ZYF Views(...) Comments(...) Edit 收藏