[算法练习]最长公共子序列

题目说明：

程序代码：

#include <gtest/gtest.h>
#include <vector>
using namespace std;

enum DirectionType
{
TypeUp,
TypeLeftUp,
TypeLeft
};

int TMaxVal(int A, int B, int C, DirectionType& index)
{
int nVal = A;
index = TypeUp;

if (B > nVal)
{
nVal = B;
index = TypeLeftUp;
}

if (C > nVal)
{
nVal = C;
index = TypeLeft;
}

return nVal;
}

// 按照上、左上、左的比较顺序
string GetLCS(const string& strA, const string& strB)
{
int nLengthA = strA.length();
int nLengthB = strB.length();

if (!nLengthA || !nLengthB)
{
return "";
}

struct RecordInfo
{
char Direction;
char Count;
};

RecordInfo* arrRecordInfo = new RecordInfo[(nLengthA + 1) * (nLengthB+1)];
memset(arrRecordInfo, 0, (nLengthA + 1) * (nLengthB + 1) * sizeof(RecordInfo));

for (int i = 1; i <= nLengthA; ++i)
{
for (int j = 1; j <= nLengthB; ++j)
{
int nNewVal = 0;
DirectionType nDirect;
if (strA[i-1] == strB[j-1])
{
nNewVal = TMaxVal(
arrRecordInfo[(i-1)*(nLengthB+1) + j].Count,
arrRecordInfo[(i-1)*(nLengthB+1) + j-1].Count + 1,
arrRecordInfo[i*(nLengthB+1) + j-1].Count,
nDirect);
}
else
{
nNewVal = TMaxVal(
arrRecordInfo[(i-1)*(nLengthB+1) + j].Count,
arrRecordInfo[(i-1)*(nLengthB+1) + j-1].Count,
arrRecordInfo[i*(nLengthB+1) + j-1].Count,
nDirect);
}

arrRecordInfo[i*(nLengthB+1) + j].Count = nNewVal;
arrRecordInfo[i*(nLengthB+1) + j].Direction = nDirect;
}
}

string strValue;
int i = nLengthA;
int j = nLengthB;
while ((i > 0) && (j > 0))
{
int nDirect = arrRecordInfo[i*(nLengthB+1) + j].Direction;
if (TypeLeftUp == nDirect)
{
if (strA[i-1] == strB[j-1])
{
strValue += strA[i-1];
}

--i;
--j;
}
else if(TypeUp == nDirect)
{
--i;
}
else if(TypeLeft == nDirect)
{
--j;
}
}

reverse(strValue.begin(),strValue.end());

return strValue;
}

TEST(Algo, tLongestCommonSequence)
{
//
// "" ""
// abcdefg   bdacafg
// abcabcagc abcdcagb

vector<string> result;
ASSERT_EQ(GetLCS("",""),"");
ASSERT_EQ(GetLCS("abcdefg","bdacafg"), "acfg");
}