【算法Everyday】第三日 KMP算法

题目

你知道的。

分析

分析不来。

代码

void OutputArray(int* pArr, int iLen)
{
    for (int i = 0; i < iLen; i++)
    {
        printf("%d\t", pArr[i]);
    }
    printf("\n");
}

void GetNextValue(char const* szPattern, int iLen, int* pNextArr)
{
    int i = 0;
    pNextArr[i] = -1;
    int j = -1;
    while (i < iLen - 1)
    {
        if (j == -1 || szPattern[i] == szPattern[j])
        {
            ++i;
            ++j;
            if (szPattern[i] != szPattern[j])
                pNextArr[i] = j;
            else
                pNextArr[i] = pNextArr[j];
        }
        else
            j = pNextArr[j];
    }
}

int KMP(const char * szTarget, const char * szPattern)
{
    int iSrcLen = strlen(szTarget);
    int iPatternLen = strlen(szPattern);

    int* pNextArr = new int[iPatternLen];
    GetNextValue(szPattern, iPatternLen, pNextArr);
    OutputArray(pNextArr, iPatternLen);

    int targetIndex = 0;
    int patternIndex = 0;
    while (targetIndex < iSrcLen && patternIndex < iPatternLen)
    {
        if (patternIndex == -1 || szTarget[targetIndex] == szPattern[patternIndex])
        {
            ++targetIndex;
            ++patternIndex;
        }
        else
        {
            patternIndex = pNextArr[patternIndex];
        }
    }

    delete[] pNextArr;

    if (patternIndex >= iPatternLen)
        return targetIndex - iPatternLen;
    else
        return -1;
}

void GetNextValue2(char const* szPattern, int iLen, int* pNextArr)
{
    int index = 0;
    pNextArr[0] = -1;
    for (int i = 1; i < iLen; ++i)
    {
        index = pNextArr[i - 1];
        while (index >= 0 && szPattern[index + 1] != szPattern[i])
        {
            index = pNextArr[index];
        }
        if (szPattern[index + 1] == szPattern[i])
        {
            pNextArr[i] = index + 1;
        }
        else
        {
            pNextArr[i] = -1;
        }
    }
}

int KMP2(const char* szTarget, const char* szPattern)
{
    const int iSrcLen = strlen(szTarget);
    const int iPatternLen = strlen(szPattern);

    int* pNextArr = new int[iPatternLen];

    GetNextValue2(szPattern, iPatternLen, pNextArr);
    OutputArray(pNextArr, iPatternLen);

    int patternIndex = 0;
    int targetIndex = 0;
    while (patternIndex < iPatternLen && targetIndex < iSrcLen)
    {
        if (szTarget[targetIndex] == szPattern[patternIndex])
        {
            ++targetIndex;
            ++patternIndex;
        }
        else if (patternIndex == 0)
        {
            ++targetIndex;
        }
        else
        {
            patternIndex = pNextArr[patternIndex - 1] + 1;
        }
    }

    delete[] pNextArr;

    if (patternIndex == iPatternLen)
        return targetIndex - patternIndex;
    else
        return -1;
}