CodeLibrary/StringProcessing/KMP String Matching.cpp at master · sayedppqq/CodeLibrary · GitHub

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#include<bits/stdc++.h>
using namespace std;
#define  FIO        ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define  all(v)     v.begin(),v.end()
#define  rall(v)    v.rbegin(),v.rend()
#define MEM(a,x)    memset(a,x,sizeof(a))
#define pi          acos(-1.0)
#define  ll     long long
#define  pb     push_back
#define  mp     make_pair
#define  pii    pair< int,int >
#define  pll    pair< ll,ll >
#define  vii    vector< int >
#define  vll    vector< ll >
#define  vpi    vector< pii >
#define  MX     100005
#define  EPS    1e-12
#define  ss     second
#define  ff     first
int cases=1;
#ifdef ppqq
     #define debug(...) __f(#__VA_ARGS__, __VA_ARGS__)
    template < typename Arg1 >
    void __f(const char* name, Arg1&& arg1){
        cerr << name << " is " << arg1 << std::endl;
    }
    template < typename Arg1, typename... Args>
    void __f(const char* names, Arg1&& arg1, Args&&... args){
        const char* comma = strchr(names+1, ',');
        cerr.write(names, comma - names) << " is " << arg1 <<"  ";
        __f(comma+1, args...);
    }
#else
    #define debug(...)
#endif
///******************************************START******************************************
class KMP
{
    public:
    vector<int> prefix_function(string s) {
        ///https://cp-algorithms.com/string/prefix-function.html#final-algorithm
        int n = (int)s.length();
        vector<int> lps(n);
        for (int i = 1; i < n; i++) {
            int j = lps[i-1];
            while (j > 0 && s[i] != s[j])
                j = lps[j-1];
            if (s[i] == s[j])
                j++;
            lps[i] = j;
        }
        return lps;
    }
    ll kmp(string text,string pattern)
    {
        ll cnt=0;
        vii lps;
        lps=prefix_function(pattern);
        int i=0,j=0;
        while(i<text.size())
        {
            if(text[i]==pattern[j])
            {
                i++;
                j++;
            }
            else
            {
                if(j!=0) j=lps[j-1];
                else i++;
            }
            if(j==pattern.size())
            {
                cnt++;
                j=lps[j-1];
            }
        }

        return cnt;
    }
};
KMP obj;
int main()
{
   //freopen ("output.txt","w",stdout);
   //freopen ("input.txt","r",stdin);
    FIO;
    string pat,text;
    cin>>text>>pat;
    cout<<obj.kmp(text,pat); ///this will return how many pat matches in text
}