hdu 3722 Card Game (有向环覆盖，拆点，二分图最佳匹配，KM算法)
题意：n个串，a串放在b串前面的val值是“The score of sticking two cards is the longest common prefix of the second card and the reverse of the first card”.问如何放使得总的val最大。
思路：先暴力处理出每两个的权值。。2002001000的复杂度。。还是可以接受的。。
然后把每个串看成了一个点，由于一个串最多可以被放在前面一次，被放在后面一次，所以可以类比图论中的环的入度和出度为1.
然后跑一遍KM. 1A,开心。
1/* ***********************************************
2Author :111qqz
3Created Time :2016年06月02日 星期四 23时37分55秒
4File Name :code/hdu/3722.cpp
5************************************************ */
6
7#include <cstdio>
8#include <cstring>
9#include <iostream>
10#include <algorithm>
11#include <vector>
12#include <queue>
13#include <set>
14#include <map>
15#include <string>
16#include <cmath>
17#include <cstdlib>
18#include <ctime>
19#define fst first
20#define sec second
21#define lson l,m,rt<<1
22#define rson m+1,r,rt<<1|1
23#define ms(a,x) memset(a,x,sizeof(a))
24typedef long long LL;
25#define pi pair < int ,int >
26#define MP make_pair
27
28using namespace std;
29const double eps = 1E-8;
30const int dx4[4]={1,0,0,-1};
31const int dy4[4]={0,-1,1,0};
32const int inf = 0x3f3f3f3f;
33const int N=205;
34int n;
35char st[N][1005];
36int w[N][N];
37int link[N];
38int lx[N],ly[N];
39bool visx[N],visy[N];
40int slk[N];
41int solve(string a,string b)
42{
43 int la = a.length();
44 int lb = b.length();
45 int len = min(la,lb);
46 int res = 0 ;
47 for ( int i = 0 ; i < len ; i++)
48 {
49 if (b[i]==a[la-1-i]) res++;
50 else break;
51 }
52 return res;
53}
54
55bool find( int u)
56{
57 // cout<<"u:"<<u<<endl;
58 visx[u] = true;
59 for ( int v = 1 ; v <= n ; v++)
60 {
61 if (visy[v]) continue;
62
63 int tmp = lx[u] + ly[v] - w[u][v];
64 if (tmp==0)
65 {
66 visy[v] = true;
67 if (link[v]==-1||find(link[v]))
68 {
69 link[v] = u ;
70 return true;
71 }
72 }else if (tmp<slk[v]) slk[v] = tmp;
73 }
74 return false;
75}
76int KM()
77{
78 ms(lx,0);
79 ms(ly,0);
80 ms(link,-1);
81
82 for ( int i = 1 ; i <= n ; i++)
83 for ( int j = 1 ; j <= n ; j++ )
84 lx[i] = max(lx[i],w[i][j]);
85
86 for ( int i = 1; i <= n ; i++)
87 {
88 ms(slk,0x3f);
89
90 while (1)
91 {
92 ms(visx,false);
93 ms(visy,false);
94
95 if (find(i)) break;
96
97 int d = inf;
98
99 for ( int j = 1 ; j <= n ; j++)
100 if (!visy[j]&&slk[j]<d) d= slk[j];
101
102 for ( int j = 1 ; j <= n ; j++)
103 if (visx[j]) lx[j]-=d;
104
105 for ( int j = 1 ; j <= n ; j++)
106 if (visy[j]) ly[j]+=d ; else slk[j]-=d;
107 }
108 }
109 int res = 0 ;
110 for ( int i = 1 ; i <= n ; i++)
111 if (link[i]>-1) res += w[link[i]][i];
112
113 return res;
114}
115int main()
116{
117 #ifndef ONLINE_JUDGE
118 freopen("code/in.txt","r",stdin);
119 #endif
120
121 while (~scanf("%d",&n))
122 {
123 for ( int i = 1 ; i <= n ; i++) scanf("%s",st[i]);
124
125 ms(w,0);
126
127 for ( int i = 1 ; i <= n ; i++)
128 for ( int j = 1 ; j <= n ; j++)
129 if (i!=j) w[i][j] = solve(string(st[i]),string(st[j]));
130
131 // for ( int i = 1 ; i <= n ; i++)
132 // for ( int j = 1 ; j <= n ; j++) if (i!=j) cout<<"w[i][j]:"<<w[i][j]<<endl;
133
134 int ans = KM();
135 printf("%d\n",ans);
136 }
137
138 #ifndef ONLINE_JUDGE
139 fclose(stdin);
140 #endif
141 return 0;
142}