[英]Longest Common Subsequence incorrect printing
I have been trying to implement the Longest Common Subsequence for a few hours now. 我已经尝试实施几个小时的最长公共子序列。 I have checked that LCSLength function returns correct length, but it is not printing the sequence correctly.
我已经检查过LCSLength函数返回正确的长度,但是它没有正确打印序列。
int max(int a , int b)
{
if(a>b)
return a;
else
return b;
}
/* The printing function that is not functioning Properly */
string backtrack(vector< vector<int> > C, string X,string Y,int i,int j)
{
if( i==0 || j==0)
return "";
else if( X[i] == Y[j])
return backtrack(C,X,Y,i-1,j-1) + X[i];
else
if( C[i][j-1] >= C[i-1][j] )
return backtrack(C,X,Y,i,j-1);
else
return backtrack(C,X,Y,i-1,j);
}
/* It correctly returns the subsequence length. */
int LCSLength(string s1,string s2)
{
vector< vector <int> > C (s1.size()+1 , vector<int> (s2.size() +1 ) );
int i,j;
int m = s1.size();
int n = s2.size();
for(i =0; i<=m; i++){
for( j =0; j<=n; j++){
if( i==0 || j==0)
C[i][j] = 0;
else if( s1[i-1] == s2[j-1] )
C[i][j] = C[i-1][j-1] +1;
else
C[i][j] = max(C[i][j-1],C[i-1][j]);
}
}
cout << backtrack(C,s1,s2,m,n);
return C[m][n];
}
I am following pseudocode given here: http://en.wikipedia.org/wiki/Longest_common_subsequence_problem 我正在遵循此处给出的伪代码: http : //en.wikipedia.org/wiki/Longest_common_subsequence_problem
Any help you would appreciated. 任何帮助,您将不胜感激。
Tested Cases: 测试案例:
cout << LCSLength("HUMAN", "CHIMPANZEE") << endl;
returns 4 but string sequence is incorrect. 返回4,但字符串顺序不正确。
cout << LCSLength("AAACCGTGAGTTATTCGTTCTAGAA","CACCCCTAAGGTACCTTTGGTTC") << endl;
returns 14 返回14
Thanks. 谢谢。
I'm guessing that since your stopping condition is : 我猜是因为您的停车条件是:
if( i==0 || j==0)
return "";
You can never reach the character at X[0] or Y[0]. 您永远无法到达X [0]或Y [0]处的字符。 Your example of wrong printout ("MAN" instead of "HMAN") matches this, as H is the first char.
您的错误打印输出示例(“ MAN”而不是“ HMAN”)与此匹配,因为H是第一个字符。
Note that the wiki value you link is defining the strings as X[1..m] and Y[1..n]
, which is probably not the intuitive way to do this in c++. 请注意,您链接的Wiki值将字符串定义为
X[1..m] and Y[1..n]
,这可能不是在c ++中实现此目的的直观方法。
Try switching to -1 as stopping condition, or pad your strings at the beginning. 尝试切换到-1作为停止条件,或在开始时填充琴弦。
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