HDU-4665 Unshuffle 搜索 | 2-SAT

　　题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4665

　　本题的2-SAT建图颇为复杂，有时间再来填坑（自己写的一直挂着，标程建图太复杂了）。。。然后用暴力搜索，用一个栈保存第一个序列就可以了，因为题目是SPG，并且重复的最多只有四个，所以搜索很好过。。

 1 //STATUS:C++_AC_62MS_276KB

 2 #include <functional>

 3 #include <algorithm>

 4 #include <iostream>

 5 //#include <ext/rope>

 6 #include <fstream>

 7 #include <sstream>

 8 #include <iomanip>

 9 #include <numeric>

10 #include <cstring>

11 #include <cassert>

12 #include <cstdio>

13 #include <string>

14 #include <vector>

15 #include <bitset>

16 #include <queue>

17 #include <stack>

18 #include <cmath>

19 #include <ctime>

20 #include <list>

21 #include <set>

22 #include <map>

23 using namespace std;

24 //#pragma comment(linker,"/STACK:102400000,102400000")

25 //using namespace __gnu_cxx;

26 //define

27 #define pii pair<int,int>

28 #define mem(a,b) memset(a,b,sizeof(a))

29 #define lson l,mid,rt<<1

30 #define rson mid+1,r,rt<<1|1

31 #define PI acos(-1.0)

32 //typedef

33 typedef __int64 LL;

34 typedef unsigned __int64 ULL;

35 //const

36 const int N=2010;

37 const int INF=0x3f3f3f3f;

38 const int MOD= 1000000007,STA=8000010;

39 const LL LNF=1LL<<55;

40 const double EPS=1e-9;

41 const double OO=1e30;

42 const int dx[4]={-1,0,1,0};

43 const int dy[4]={0,1,0,-1};

44 const int day[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};

45 //Daily Use ...

46 inline int sign(double x){return (x>EPS)-(x<-EPS);}

47 template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}

48 template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}

49 template<class T> inline T lcm(T a,T b,T d){return a/d*b;}

50 template<class T> inline T Min(T a,T b){return a<b?a:b;}

51 template<class T> inline T Max(T a,T b){return a>b?a:b;}

52 template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}

53 template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}

54 template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}

55 template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}

56 //End

57 

58 int num[N],sta[N],vis[N];

59 int T,n,top1,top2,mid;

60 

61 bool dfs(int u)

62 {

63     if(top2==mid)return true;

64     if(top1<mid){

65         vis[u]=0;

66         sta[top1++]=num[u];

67         if(dfs(u+1))return true;

68         top1--;

69     }

70     if(num[u]==sta[top2]){

71         vis[u]=1;

72         top2++;

73         if(dfs(u+1))return true;

74         vis[u]=0;

75         top2--;

76     }

77     return false;

78 }

79 

80 int main(){

81  //   freopen("in.txt","r",stdin);

82     int i,j;

83     scanf("%d",&T);

84     while(T--)

85     {

86         scanf("%d",&n);

87         mid=n>>1;

88         for(i=0;i<n;i++)

89             scanf("%d",&num[i]);

90 

91         top1=top2=0;

92         dfs(0);

93 

94         for(i=0;i<n;i++)

95             printf("%d",vis[i]);

96         putchar('\n');

97     }

98     return 0;

99 }

 

2-SAT(WA):

  1 /*   WA   */

  2 #include <functional>

  3 #include <algorithm>

  4 #include <iostream>

  5 //#include <ext/rope>

  6 #include <fstream>

  7 #include <sstream>

  8 #include <iomanip>

  9 #include <numeric>

 10 #include <cstring>

 11 #include <cassert>

 12 #include <cstdio>

 13 #include <string>

 14 #include <vector>

 15 #include <bitset>

 16 #include <queue>

 17 #include <stack>

 18 #include <cmath>

 19 #include <ctime>

 20 #include <list>

 21 #include <set>

 22 #include <map>

 23 using namespace std;

 24 //#pragma comment(linker,"/STACK:102400000,102400000")

 25 //using namespace __gnu_cxx;

 26 //define

 27 #define pii pair<int,int>

 28 #define mem(a,b) memset(a,b,sizeof(a))

 29 #define lson l,mid,rt<<1

 30 #define rson mid+1,r,rt<<1|1

 31 #define PI acos(-1.0)

 32 //typedef

 33 typedef __int64 LL;

 34 typedef unsigned __int64 ULL;

 35 //const

 36 const int N=2010;

 37 const int INF=0x3f3f3f3f;

 38 const int MOD= 1000000007,STA=8000010;

 39 const LL LNF=1LL<<55;

 40 const double EPS=1e-9;

 41 const double OO=1e30;

 42 const int dx[4]={-1,0,1,0};

 43 const int dy[4]={0,1,0,-1};

 44 const int day[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};

 45 //Daily Use ...

 46 inline int sign(double x){return (x>EPS)-(x<-EPS);}

 47 template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}

 48 template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}

 49 template<class T> inline T lcm(T a,T b,T d){return a/d*b;}

 50 template<class T> inline T Min(T a,T b){return a<b?a:b;}

 51 template<class T> inline T Max(T a,T b){return a>b?a:b;}

 52 template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}

 53 template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}

 54 template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}

 55 template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}

 56 //End

 57 

 58 struct Edge{

 59     int u,v;

 60 }e[N<<4];

 61 

 62 int first[N<<1],next[N<<4],vis[N<<1],S[N<<1];

 63 int num[N];

 64 int T,n,mt,cnt;

 65 

 66 void adde(int a,int b)

 67 {

 68     e[mt].u=a,e[mt].v=b;

 69     next[mt]=first[a];first[a]=mt++;

 70 }

 71 

 72 int dfs(int u)

 73 {

 74     if(vis[u^1])return 0;

 75     if(vis[u])return 1;

 76     int i;

 77     vis[u]=1;

 78     S[cnt++]=u;

 79     for(i=first[u];i!=-1;i=next[i]){

 80         if(!dfs(e[i].v))return 0;

 81     }

 82     return 1;

 83 }

 84 

 85 int Twosat()

 86 {

 87     int i,j;

 88     for(i=0;i<n;i+=2){

 89         if(vis[i] || vis[i^1])continue;

 90         cnt=0;

 91         if(!dfs(i)){

 92             while(cnt)vis[S[--cnt]]=0;

 93             if(!dfs(i^1))return 0;

 94         }

 95     }

 96     return 1;

 97 }

 98 

 99 int cnt2[N],tot[N],w[N][4];

100 void Init()

101 {

102     int i,j,t;

103     mt=0;mem(vis,0);

104     mem(first,-1);

105     mem(tot,0);

106     for(i=0;i<n;i++)w[num[i]][tot[num[i]]++]=i;

107     mem(cnt2,0);

108     for(i=0;i<n;i++){

109         t=num[i];

110         cnt2[t]++;

111         if(cnt2[t]==1){

112             adde((i<<1)^1,i<<1);

113             adde(i<<1,(w[t][tot[t]-1]<<1)^1);

114             adde(w[t][tot[t]-1]<<1,(i<<1)^1);

115             if(tot[t]==4){

116                 for(j=w[t][1]+1;j<n;j++){

117                     if(w[num[j]][1]==j && w[num[j]][0]<j && w[num[j]][0]>i){

118                         adde(i<<1,(w[t][1]<<1)^1);

119                         break;

120                     }

121                 }

122             }

123         }

124         else if(cnt2[t]==3){

125             adde(w[t][1]<<1,(w[t][2]<<1)^1);

126             adde((w[t][1]<<1)^1,w[t][2]<<1);

127             adde(w[t][2]<<1,(w[t][1]<<1)^1);

128             adde((w[t][2]<<1)^1,w[t][1]<<1);

129         }

130     }

131 }

132 

133 int main(){

134     freopen("in.txt","r",stdin);

135     int i,j;

136     scanf("%d",&T);

137     while(T--)

138     {

139         scanf("%d",&n);

140         for(i=0;i<n;i++)

141             scanf("%d",&num[i]);

142 

143         Init();

144         n<<=1;

145         int t=Twosat();

146     //    printf("%d\n",t);

147 

148         for(i=0;i<n;i+=2)

149             printf("%d",vis[i]);

150         putchar('\n');

151     }

152     return 0;

153 }

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