POJ 3461 Oulipo

利用KMP算法查找字符串中字串出现的次数

 

#include <iostream>
#include <vector>
#include <string>

using namespace std;

int* computeOverlap(string& s)
{
    int length = s.length();

    if(length == 0)
        return NULL;

    int* overlayValue = new int[length];
    overlayValue[0] = -1;

    for(int i=1; i<length; i++)
    {
        int index = overlayValue[i-1];

        while(index>=0 && s[index+1] != s[i])
        {
            index = overlayValue[index];
        }

        if(s[index+1] == s[i])
        {
            overlayValue[i] = index+1;
        }
        else
        {
            overlayValue[i] = -1;
        }
    }

    return overlayValue;
}

int KMP_Match(string& w, string& t)
{
    int matchCount = 0;
    int* overlayValue = computeOverlap(w);

    int wLen = w.length();
    int tLen = t.length();

    int wIndex = 0;
    int tIndex = 0;

    while(wIndex < wLen && tIndex < tLen)
    {
        if(w[wIndex] == t[tIndex])
        {
            if(wIndex == wLen-1)
            {
                matchCount++;
                
                if(wIndex == 0)
                    wIndex = -1;
                else
                    wIndex = overlayValue[wIndex];

            }
            wIndex++;
            tIndex++;
        }

        else if(wIndex == 0)
        {
            tIndex++;
        }

        else
        {
            wIndex = overlayValue[wIndex-1]+1;
        }

    }

    delete[] overlayValue;

    return matchCount;
}

int main()
{
    int count = 0;
    cin>>count;
    
    vector<string> W;
    vector<string> T;
    W.resize(count);
    T.resize(count);

    for(int i=0; i<count; i++)
    {
        cin>>W[i];
        cin>>T[i];
    }

    for(int i=0; i<count; i++)
    {
        cout<<KMP_Match(W[i],T[i])<<endl;
    }

    return 0;
}