Manachar’s Algorithm

resources:

HackerEarth

Tushar Roy 

Manacher's Algorithm - Finding all sub-palindromes 

IDeserve 

LeetCodeProblem

Visualize 

GFG 

Problems:

LPS - Longest Palindromic Substring 

CF blog  

Cf blog 2 

Build a Palindrome 

 Implementation:

	#include <bits/stdc++.h>
	using namespace std;
	#define INF 1<<30
	#define endl '\n'
	#define maxn 1000005
	#define tc printf("Case %d: ", cs)
	#define tcn printf("Case %d:\n", cs);
	#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	typedef long long ll;
	const double PI = acos(-1.0);
	#define dbg1(x) cerr << #x << " = " << x << endl;
	#define dbg2(x, y) cerr << #x << " = " << x << ", " << #y << " = " << y << endl;
	#define dbg3(x, y, z) cerr << #x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = " << z << endl;
	#define dbg4(w,x, y, z) cerr << #w << " = " << w << ", " <<#x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = " << z << endl;
	template < typename F, typename S >
	ostream& operator << ( ostream& os, const pair< F, S > & p ) {
	return os << "(" << p.first << ", " << p.second << ")";
	}
	template < typename T >
	ostream &operator << ( ostream & os, const vector< T > &v ) {
	os << "{";
	for (auto it = v.begin(); it != v.end(); ++it) {
	if ( it != v.begin() ) os << ", ";
	os << *it;
	}
	return os << "}";
	}
	template < typename T >
	ostream &operator << ( ostream & os, const set< T > &v ) {
	os << "[";
	for (auto it = v.begin(); it != v.end(); ++it) {
	if ( it != v.begin()) os << ", ";
	os << *it;
	}
	return os << "]";
	}
	template < typename F, typename S >
	ostream &operator << ( ostream & os, const map< F, S > &v ) {
	os << "[";
	for (auto it = v.begin(); it != v.end(); ++it) {
	if ( it != v.begin() ) os << ", ";
	os << it -> first << " = " << it -> second ;
	}
	return os << "]";
	}
	#define dbg(args...) do {cerr << #args << " : "; faltu(args); } while(0)
	clock_t tStart = clock();
	#define timeStamp dbg("Execution Time: ", (double)(clock() - tStart)/CLOCKS_PER_SEC)
	void faltu () { cerr << endl; }
	template <typename T>
	void faltu( T a[], int n ) {
	for (int i = 0; i < n; ++i) cerr << a[i] << ' ';
	cerr << endl;
	}
	template <typename T, typename ... hello>
	void faltu( T arg, const hello &... rest) { cerr << arg << ' '; faltu(rest...); }
	// Program showing a policy-based data structure.
	#include <ext/pb_ds/assoc_container.hpp> // Common file
	#include <ext/pb_ds/tree_policy.hpp>
	#include <functional> // for less
	#include <iostream>
	using namespace __gnu_pbds;
	using namespace std;
	// GNU link : https://goo.gl/WVDL6g
	typedef tree<int, null_type, less_equal<int>, rb_tree_tag,
	tree_order_statistics_node_update>
	new_data_set;
	/**___________________________________________________**/
	const int N = 1e6 + 5;
	int P[2 * N];
	string convertToNewString(const string &s)
	{
	string nwS = "@";
	for (int i = 0; i < (int)s.size(); i++) {
	nwS += "#" + s.substr(i, 1);
	}
	nwS += "#$";
	return nwS;
	}
	string lps(const string &s)
	{
	string Q = convertToNewString(s);
	int c = 0, r = 0; /// current center, right limit
	for (int i = 1; i < (int)Q.size() - 1; i++) {
	// find the corresponding letter in the palindrome substring
	int iMirror = c - (i - c);
	if (r > i) {
	P[i] = min(r - i, P[iMirror]);
	}
	// expanding around center i
	while (Q[i + 1 + P[i]] == Q[i - 1 - P[i]]) {
	P[i]++;
	}
	// update c,r in case if the palindrome centered at i expands past r
	if (i + P[i] > r) {
	c = i; // next center
	r = i + P[i];
	}
	}
	// Find the longest Palindrome length in p;
	int maxPalindrome = 0;
	int centerIndex = 0;
	for (int i = 1; i < (int)Q.size() - 1; i++) {
	if (P[i] > maxPalindrome) {
	maxPalindrome = P[i];
	centerIndex = i;
	}
	}
	cout << maxPalindrome << "\n";
	return s.substr((centerIndex - 1 - maxPalindrome) / 2, maxPalindrome);
	}
	int main()
	{
	FASTIO
	///*
	#ifndef ONLINE_JUDGE
	freopen("in.txt", "r", stdin);
	freopen("out.txt", "w", stdout);
	freopen("error.txt", "w", stderr);
	#endif
	//*/
	//string s = "kiomaramol\n";
	string s;
	cin >> s;
	cout << lps(s);
	return 0;
	}

view raw manachar.cpp hosted with ❤ by GitHub

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