[POJ 1934] Trip

[题目链接]

        http://poj.org/problem?id=1934

[算法]

        先用dp求出LCS，然后搜索即可，注意加上一些剪枝

[代码]

        

#include <algorithm>  
#include <bitset>  
#include <cctype>  
#include <cerrno>  
#include <clocale>  
#include <cmath>  
#include <complex>  
#include <cstdio>  
#include <cstdlib>  
#include <cstring>  
#include <ctime>  
#include <deque>  
#include <exception>  
#include <fstream>  
#include <functional>  
#include <limits>  
#include <list>  
#include <map>  
#include <iomanip>  
#include <ios>  
#include <iosfwd>  
#include <iostream>  
#include <istream>  
#include <ostream>  
#include <queue>  
#include <set>  
#include <sstream>  
#include <stdexcept>  
#include <streambuf>  
#include <string>  
#include <utility>  
#include <vector>  
#include <cwchar>  
#include <cwctype>  
#include <stack>  
#include <limits.h> 
using namespace std;
#define MAXLEN 85

int i,j,la,lb,len,l;
string a,b;
int f[MAXLEN][MAXLEN],pa[MAXLEN][MAXLEN],pb[MAXLEN][MAXLEN];
string q[1010];

inline void dfs(int dep,int pos1,int pos2,string t)
{
        int i;
        if (dep > len) q[++l] = t;
        if (pos1 < 0 || pos2 < 0) return;
        if (f[pos1][pos2] != len - dep + 1) return;
        if (dep + pos1 < len || dep + pos2 < len) return; 
        if (l >= 1000) return; 
        for (i = 0; i < 26; i++) 
        {
                if (l >= 1000) return;
                if (pa[i][pos1] != -1 && pb[i][pos2] != -1)
                        dfs(dep + 1,pa[i][pos1] - 1,pb[i][pos2] - 1,(char)(i + 'a') + t);
        }
}

int main() 
{
        
        cin.tie(0);
        ios :: sync_with_stdio(0);
        while (cin >> a)
        {
                cin >> b;
                la = a.size();
                lb = b.size();
                for (i = 0; i < la; i++)
                {
                        for (j = 0; j < lb; j++)
                        {
                                f[i][j] = 0;
                        }
                }
                for (i = 0; i < la; i++)
                {
                        for (j = 0; j < lb; j++)
                        {
                                if (a[i] == b[j]) 
                                {
                                        if (i >= 1 && j >= 1) f[i][j] = f[i - 1][j - 1] + 1;
                                        else f[i][j] = (a[i] == b[j]);
                                }
                                if (i >= 1) f[i][j] = max(f[i][j],f[i - 1][j]);
                                if (j >= 1) f[i][j] = max(f[i][j],f[i][j - 1]);
                        }
                }
                for (i = 0; i < 26; i++)
                {
                        for (j = 0; j < la; j++)
                        {
                                pa[i][j] = -1;
                        }
                }
                for (i = 0; i < 26; i++)
                {
                        for (j = 0; j < la; j++)
                        {
                                if (a[j] == 'a' + i) pa[i][j] = j;
                                else if (j > 0) pa[i][j] = pa[i][j - 1];    
                        }    
                } 
                for (i = 0; i < 26; i++)
                {
                        for (j = 0; j < lb; j++)
                        {
                                pb[i][j] = -1;
                        }
                }
                for (i = 0; i < 26; i++)
                {
                        for (j = 0; j < lb; j++)
                        {
                                if (b[j] == 'a' + i) pb[i][j] = j;
                                else if (j > 0) pb[i][j] = pb[i][j - 1]; 
                        }
                }
                len = f[la - 1][lb - 1];
                l = 0;
                dfs(1,la - 1,lb - 1,"");
                sort(q+1,q+l+1);
                for (i = 1; i <= l; i++) cout<< q[i] << endl;
        }
        
        return 0;
    
}