SPOJ/MAXMATCH.cpp at master · adityaagg09/SPOJ · GitHub

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// Maximum Self-Matching


	#include <bits/stdc++.h>
	#include <cstdio>
	#include <cstring>
	#include <cmath>
	#include <cstring>
	#include <chrono>
	#include <complex>
	#define ll long long
	#define ld long double
	#define vi vector<int>
	#define vll vector<ll>
	#define vvi vector < vi >
	#define pii pair<int,int>
	#define pll pair<long long, long long>
	#define mod 1000000007
	#define inf 1000000000000000001;
	#define all(c) c.begin(),c.end()
	#define mp(x,y) make_pair(x,y)
	#define mem(a,val) memset(a,val,sizeof(a))
	#define eb emplace_back
	#define pb push_back
	#define f first
	#define s second

	using namespace std;

		#define PI acos(-1.0)
		#define base complex<double>
		void fft(vector<base> &a,bool invert)
		{

			int n=a.size(),i,j;

			for(i=1,j=0;i<n;++i)	//Bit reverse
			{
				int bit=n>>1;
				for(;j>=bit;bit>>=1)
					j=j-bit;
				j=j+bit;
				if(i<j)
					swap(a[i],a[j]);
			}


			for(int len=2;len<=n;len<<=1)
			{
				ld ang=2*PI/len*(invert?-1:1);
				base wlen(cos(ang),sin(ang));
				for(i=0;i<n;i+=len)
				{
					base w(1);
					for(int j=0;j<len/2;++j)
					{
						base u=a[i+j],v=a[i+j+len/2]*w;
						a[i+j]=u+v;
						a[i+j+len/2]=u-v;
						w=w*wlen;
					}
				}
			}

			if(invert)
			{
				for(i=0;i<n;++i)
					a[i]/=n;
			}
		}
		vector<ll> res,a,b;

		void mul(const vector<ll> &a,const vector<ll> &b)
		{
			vector<base> fa(a.begin(),a.end()),fb(b.begin(),b.end());
			size_t n=1;
			int i;
			while(n<max(a.size(),b.size())) n<<=1;
			n<<=1;
			fa.resize(n),fb.resize(n);
			fft(fa,false);fft(fb,false);
			for(i=0;i<n;++i)
			{
				fa[i]=fa[i]*fb[i];
			}
			fft(fa,true);
			res.resize(n);
			for(i=0;i<n;++i)
				res[i]=(ll)(fa[i].real()+0.5);
		}

	int res2[1000001];

	int main()
	{
		std::ios::sync_with_stdio(false);
		int T;
		T=1;
		// cin.ignore(); must be there when using getline(cin, s)
		while(T--)
		{
			string s;
			int n,i,j;
			cin>>s;
			n=s.length();

			a.resize(n);
			b.resize(n);

			res.clear();
			for(i=0;i<n;++i)
			{
				if(s[i]=='a')
					a[i]=b[n-1-i]=1;
				else
					a[i]=b[n-1-i]=0;
			}
			mul(a,b);
			for(i=1;i<n;++i)
			{
				res2[i]+=res[n-1+i];
			}

			res.clear();
			for(i=0;i<n;++i)
			{
				if(s[i]=='b')
					a[i]=b[n-1-i]=1;
				else
					a[i]=b[n-1-i]=0;
			}
			mul(a,b);

			for(i=1;i<n;++i)
			{
				res2[i]+=res[n-1+i];
			}

			res.clear();
			for(i=0;i<n;++i)
			{
				if(s[i]=='c')
					a[i]=b[n-1-i]=1;
				else
					a[i]=b[n-1-i]=0;
			}
			mul(a,b);
			int maxi=0;
			for(i=1;i<n;++i)
			{
				res2[i]+=res[n-1+i];
				maxi=max(maxi,res2[i]);
			}
			cout<<maxi<<endl;
			for(i=1;i<n;++i)
			{
				if(maxi==res2[i])
					cout<<i<<endl;
			}

		}
		return 0;
	}