Codeforces_CompCodes/stringmatching(kmp).cpp at main · DivyanshGarg380/Codeforces_CompCodes · GitHub

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#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include<cmath>
#include<string>
#define pb push_back
#define ll long long
#define ull unsigned long long
#define deb(x) cerr<<#x<<" "<<x<<"\n"
#define debi cerr<<"hey sparky\n"
#define x first
#define y second
#define fast ios::sync_with_stdio(0),cin.tie(0),cout.tie(0)
#define eps (double)1e-9
#define all(x) x.begin(),x.end()
#define int long long
using namespace std;
using namespace __gnu_pbds;
typedef tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update> pdbs;

void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
//void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifndef ONLINE_JUDGE
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif

// look for  all edge cases
//search for a pattern


//kmp

int n,m;
string s,t;
vector<int> kmp_array;


signed main() {
	ios::sync_with_stdio(0);
	cout.tie(0);
	cin.tie(0);

	cin >> s >> t;

	n = s.size();
	m = t.size();


	kmp_array.resize(m, 0);

	int j =0;
	for(int i =1 ; i < m; i++){
		if(t[j] == t[i]){
			kmp_array[i] = j+1;
			j++;
		}
		else{
			if(j == 0)
				continue;

			while(j != 0 && t[j] != t[i]){
				j = kmp_array[j-1];
				if(t[j] == t[i]){
					kmp_array[i] = j+1;
					j += 1;
					break;
				}
			}
		}
	}

	//debug(kmp_array);

	j = 0;

	int cnt = 0;

	for(int i =0 ; i < n ; i++){
		if(s[i] == t[j]){
			j++;
			if(j == m){
				cnt++;
				j--;
				if(j >= 1)
					j= kmp_array[j];

			}
		}
		else{
			if(j == 0)
				continue;
			while(j != 0){
				j = kmp_array[j-1];
				if(t[j] == s[i]){
					j++;
					break;
				}
			}
		}
	}

	cout<<cnt;


	return 0;
}