Circular Palindromes
Problem Statement :
A palindrome is a string that reads the same from left to right as it does from right to left. Given a string, , S of N lowercase English letters, we define a k-length rotation as cutting the first kcharacters from the beginning of S and appending them to the end of S. For each S, there are N possible k-length rotations (where 0 <= K < N ). See the Explanation section for examples. Given N and S, find all N k-length rotations of S; for each rotated string, Sk, print the maximum possible length of any palindromic substring of Sk on a new line. Input Format The first line contains an integer, N (the length of S ). The second line contains a single string, S. Constraints 1 <= N <= 5* 10^5 0 <= K < N S is comprised of lower case English letters. Output Format There should be N lines of output, where each line k contains an integer denoting the maximum length of any palindromic substring of rotation Sk.
Solution :
Solution in C :
In C++ :
#include <algorithm>
#include <iostream>
#include <cassert>
#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <queue>
#include <map>
#include <set>
using namespace std;
#define type(x) __typeof((x).begin())
#define foreach(i, x) for(type(x) i = (x).begin(); i != (x).end(); i++)
#define hash ___hash
typedef long long ll;
typedef pair < int, int > ii;
const int inf = 1e9 + 333;
const ll linf = 1e18 + 333;
const int N = 2e6 + 5;
int n;
char s[N];
bool h[N];
int go_odd[N], go_even[N], tmp[N << 1], rad[N << 1], ans[2][N];
void manacher() {
memset(tmp, 0, sizeof(tmp));
memset(rad, 0, sizeof(rad));
int m = n * 2 + 1;
for(int i = 0; i < m; i++)
tmp[i] = '#';
for(int i = 0; i < n; i++)
tmp[i * 2 + 1] = s[i + 1];
int i = 0, j = 0;
while(i < m) {
while(i - j >= 0 and i + j < m and tmp[i - j] == tmp[i + j])
j++;
rad[i] = j;
int k = 1;
while(rad[i - k] < rad[i] - k) {
rad[i + k] = rad[i - k];
k++;
}
i += k;
j = max(0, j - k);
}
for(int i = 1; i <= n; i++)
go_odd[i] = rad[(i - 1) * 2 + 1] / 2;//abcba --> go_odd[3] = 3
for(int i = 1; i <= n; i++)
go_even[i - 1] = rad[(i - 1) * 2] / 2;//abccba --> go_even[3] = 3
}
void solveOdd(bool w) {
int oth = 0;
set < ii > go;
for(int i = 1; i <= (n + 1) / 2; i++) {
go.insert({go_odd[i], i});
}
for(int i = 1; i <= n; i++) {
while(go.size()) {
int x = go.rbegin() -> first;
int id = go.rbegin() -> second;
if(id < i) {
go.erase(*go.rbegin());
continue;
}
int mx = (id - i + 1) * 2 - 1;
if(x > mx) {
oth = max(oth, id);
go.erase(*go.rbegin());
continue;
}
break;
}
if(go.size())
ans[w][i] = max(ans[w][i], go.rbegin() -> first);
if(oth >= i)
ans[w][i] = max(ans[w][i], (oth - i + 1) * 2 - 1);
//printf("ans[%d] = %d oth = %d\n", i, ans[w][i]);
int add = (n + 1) / 2 + i;
go.insert({go_odd[add], add});
}
}
int get(int x, int y) {
y -= x - 1;
return min(y, n - y) * 2;
}
void solveEven(bool w) {
int oth = 0;
set < ii > go;
for(int i = 1; i <= (n + 1) / 2; i++) {
go.insert({go_even[i], i});
}
for(int i = 1; i <= n; i++) {
while(go.size()) {
int x = go.rbegin() -> first;
int id = go.rbegin() -> second;
if(id < i) {
go.erase(*go.rbegin());
continue;
}
int mx = get(i, id);
if(x > mx) {
oth = max(oth, id);
go.erase(*go.rbegin());
continue;
}
break;
}
if(go.size())
ans[w][i] = max(ans[w][i], go.rbegin() -> first);
if(oth >= i)
ans[w][i] = max(ans[w][i], get(i, oth));
//printf("ans[%d] = %d\n", i, ans[w][i]);
int add = (n + 1) / 2 + i;
go.insert({go_even[add], add});
}
}
int main () {
scanf("%d %s", &n, s + 1);
for(int i = 1; i <= n; i++)
s[i + n] = s[i];
////////////////////////////////////
n *= 2;
manacher();
n /= 2;
for(int i = 1; i <= n + n; i++) {
go_odd[i] *= 2;
go_odd[i] -= 1;
go_even[i] *= 2;
}
solveOdd(0);
solveEven(0);
///////////////////////////////////
reverse(s + 1, s + n * 2 + 1);
n *= 2;
manacher();
n /= 2;
for(int i = 1; i <= n + n; i++) {
go_odd[i] *= 2;
go_odd[i] -= 1;
go_even[i] *= 2;
}
solveOdd(1);
solveEven(1);
///////////////////////////////////
printf("%d\n", max(ans[0][1], ans[1][1]));
for(int i = 2; i <= n; i++) {
printf("%d\n", max(ans[0][i], ans[1][n + 2 - i]));
}
return 0;
}
In Java :
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.InputMismatchException;
public class E2 {
InputStream is;
PrintWriter out;
String INPUT = "";
void solve()
{
int n = ni();
char[] s = ns(n);
char[] s2 = new char[2*n];
for(int i = 0;i < n;i++){
s2[i] = s2[i+n] = s[i];
}
int[] pal = palindrome(s2);
// tr(pal, pal.length, n);
long[] es = new long[16*n];
int p = 0;
for(int i = 0;i < 4*n;i+=2){
pal[i] = Math.min(pal[i], n-((n&1)^1));
es[p++] = (long)(i/2)<<32|i;
es[p++] = (long)(i/2+pal[i]/2)<<32|i;
es[p++] = (long)(i/2+n-pal[i]/2-1)<<32|i;
es[p++] = (long)(i/2+n)<<32|i;
}
for(int i = 1;i < 4*n;i+=2){
pal[i] = Math.min(pal[i], n-((n&1)));
es[p++] = (long)(i/2)<<32|i;
es[p++] = (long)(i/2+pal[i]/2)<<32|i;
es[p++] = (long)(i/2+n-pal[i]/2)<<32|i;
es[p++] = (long)(i/2+n)<<32|i;
}
Arrays.sort(es, 0, p);
MaxHeap inc = new MaxHeap(4*n+1);
MaxHeap dec = new MaxHeap(4*n+1);
MaxHeap flat = new MaxHeap(4*n+1);
int[] st = new int[4*n];
int q = 0;
for(int i = 0;i < 2*n-1;i++){
while(q < p && es[q]>>>32 <= i){
int ind = (int)es[q];
if(st[ind] == 0){
inc.add(ind, (pal[ind]&1)-2*i);
}else if(st[ind] == 1){
inc.remove(ind);
flat.add(ind, pal[ind]);
}else if(st[ind] == 2){
flat.remove(ind);
dec.add(ind, pal[ind]+2*i);
}else if(st[ind] == 3){
dec.remove(ind);
}
st[ind]++;
q++;
}
if(i >= n-1){
// tr("i", i);
int max = 0;
if(inc.size() > 0)max = Math.max(inc.max()+2*i, max);
// tr(max);
if(dec.size() > 0)max = Math.max(dec.max()-2*i, max);
// tr(max);
max = Math.max(flat.max(), max);
// tr(max);
out.println(max);
}
}
}
public static class MaxHeap {
public int[] a;
public int[] map;
public int[] imap;
public int n;
public int pos;
public static int INF = Integer.MIN_VALUE;
public MaxHeap(int m)
{
n = m+2;
a = new int[n];
map = new int[n];
imap = new int[n];
Arrays.fill(a, INF);
Arrays.fill(map, -1);
Arrays.fill(imap, -1);
pos = 1;
}
public int add(int ind, int x)
{
int ret = imap[ind];
if(imap[ind] < 0){
a[pos] = x; map[pos] = ind; imap[ind] = pos;
pos++;
up(pos-1);
}
return ret != -1 ? a[ret] : x;
}
public int update(int ind, int x)
{
int ret = imap[ind];
if(imap[ind] < 0){
a[pos] = x; map[pos] = ind; imap[ind] = pos;
pos++;
up(pos-1);
}else{
int o = a[ret];
a[ret] = x;
up(ret);
down(ret);
// if(a[ret] < o){
// up(ret);
// }else{
// down(ret);
// }
}
return x;
}
public int remove(int ind)
{
if(pos == 1)return INF;
if(imap[ind] == -1)return INF;
pos--;
int rem = imap[ind];
int ret = a[rem];
map[rem] = map[pos];
imap[map[pos]] = rem;
imap[ind] = -1;
a[rem] = a[pos];
a[pos] = INF;
map[pos] = -1;
up(rem);
down(rem);
return ret;
}
public int max() { return a[1]; }
public int argmax() { return map[1]; }
public int size() { return pos-1; }
private void up(int cur)
{
for(int c = cur, p = c>>>1;p >= 1 && a[p] < a[c];c>>>=1, p>>>=1){
int d = a[p]; a[p] = a[c]; a[c] = d;
int e = imap[map[p]]; imap[map[p]] = imap[map[c]]; imap[map[c]] = e;
e = map[p]; map[p] = map[c]; map[c] = e;
}
}
private void down(int cur)
{
for(int c = cur;2*c < pos;){
int b = a[2*c] > a[2*c+1] ? 2*c : 2*c+1;
if(a[b] > a[c]){
int d = a[c]; a[c] = a[b]; a[b] = d;
int e = imap[map[c]]; imap[map[c]] = imap[map[b]]; imap[map[b]] = e;
e = map[c]; map[c] = map[b]; map[b] = e;
c = b;
}else{
break;
}
}
}
}
public static int[] palindrome(char[] str)
{
int n = str.length;
int[] r = new int[2*n];
int k = 0;
for(int i = 0, j = 0;i < 2*n;i += k, j = Math.max(j-k, 0)){
// normally
while(i-j >= 0 && i+j+1 < 2*n && str[(i-j)/2] == str[(i+j+1)/2])j++;
r[i] = j;
// skip based on the theorem
for(k = 1;i-k >= 0 && r[i]-k >= 0 && r[i-k] != r[i]-k;k++){
r[i+k] = Math.min(r[i-k], r[i]-k);
}
}
return r;
}
void run() throws Exception
{
is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
out = new PrintWriter(System.out);
long s = System.currentTimeMillis();
solve();
out.flush();
if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
}
public static void main(String[] args) throws Exception { new E2().run(); }
private byte[] inbuf = new byte[1024];
private int lenbuf = 0, ptrbuf = 0;
private int readByte()
{
if(lenbuf == -1)throw new InputMismatchException();
if(ptrbuf >= lenbuf){
ptrbuf = 0;
try { lenbuf = is.read(inbuf); }
catch (IOException e) { throw new InputMismatchException(); }
if(lenbuf <= 0)return -1;
}
return inbuf[ptrbuf++];
}
private boolean isSpaceChar(int c)
{ return !(c >= 33 && c <= 126); }
private int skip()
{ int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }
private double nd() { return Double.parseDouble(ns()); }
private char nc() { return (char)skip(); }
private String ns()
{
int b = skip();
StringBuilder sb = new StringBuilder();
while(!(isSpaceChar(b)))
{ // when nextLine, (isSpaceChar(b) && b != ' ')
sb.appendCodePoint(b);
b = readByte();
}
return sb.toString();
}
private char[] ns(int n)
{
char[] buf = new char[n];
int b = skip(), p = 0;
while(p < n && !(isSpaceChar(b))){
buf[p++] = (char)b;
b = readByte();
}
return n == p ? buf : Arrays.copyOf(buf, p);
}
private char[][] nm(int n, int m)
{
char[][] map = new char[n][];
for(int i = 0;i < n;i++)map[i] = ns(m);
return map;
}
private int[] na(int n)
{
int[] a = new int[n];
for(int i = 0;i < n;i++)a[i] = ni();
return a;
}
private int ni()
{
int num = 0, b;
boolean minus = false;
while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
if(b == '-'){
minus = true;
b = readByte();
}
while(true){
if(b >= '0' && b <= '9'){
num = num * 10 + (b - '0');
}else{
return minus ? -num : num;
}
b = readByte();
}
}
private long nl()
{
long num = 0;
int b;
boolean minus = false;
while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
if(b == '-'){
minus = true;
b = readByte();
}
while(true){
if(b >= '0' && b <= '9'){
num = num * 10 + (b - '0');
}else{
return minus ? -num : num;
}
b = readByte();
}
}
private static void tr(Object... o)
{ System.out.println(Arrays.deepToString(o)); }
}
In C :
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void solve(char *str,int *a);
void init( int n );
void range_increment( int i, int j, int val );
int query( int i );
int max(int x,int y);
void update(int x,int y,int z);
void sort_a2(int*a,int*b,int size);
void merge2(int*a,int*left_a,int*right_a,int*b,int*left_b,int*right_b,int left_size, int right_size);
char str[1000001]={0};
int N,NN,a[2000004],tree[2000000],ans[500000],b[500000],c[500000];
int main(){
int i,j;
scanf("%d%s",&NN,str);
strncpy(str+NN,str,NN);
solve(str,a);
init(NN);
for(i=0;i<4*NN;i++)
if(a[i])
if(i%2)
update(i/2-a[i]/2,i/2+a[i]/2,a[i]);
else
update(i/2-a[i]/2,i/2+a[i]/2-1,a[i]);
for(i=0;i<NN;i++){
ans[i]=query(i);
b[i]=ans[i];
c[i]=i;
}
sort_a2(b,c,NN);
for(i=NN;i>=0;i--){
for(j=c[i];1;j=(j-1+NN)%NN)
if(ans[j]-ans[(j-1+NN)%NN]>2)
ans[(j-1+NN)%NN]=ans[j]-2;
else
break;
for(j=c[i];1;j=(j+1)%NN)
if(ans[j]-ans[(j+1)%NN]>2)
ans[(j+1)%NN]=ans[j]-2;
else
break;
}
for(i=0;i<NN;i++)
printf("%d\n",ans[i]);
return 0;
}
void solve(char *str,int *a){
char *p;
int len,R,Ri,i,j,mi;
len=strlen(str);
p=(char*)malloc(2*(len+1)*sizeof(char));
for(i=0;i<len;i++){
p[2*i]='#';
p[2*i+1]=str[i];
}
p[2*i]='#';
p[2*i+1]=0;
a[0]=R=Ri=0;
for(i=1;i<=len*2;i++)
if(i>=R){
if(p[i]!='#')
a[i]=1;
else
a[i]=0;
for(j=i+1;1;j++)
if(j<=2*len && 2*i-j>=0 && p[j]==p[2*i-j]){
if(p[j]!='#')
a[i]+=2;
}
else{
Ri=i;
R=j-1;
break;
}
}
else{
mi=2*Ri-i;
if(i+a[mi]>=R || mi==a[mi]){
a[i]=R-i;
for(j=R+1;1;j++)
if(j<=2*len && 2*i-j>=0 && p[j]==p[2*i-j]){
if(p[j]!='#')
a[i]+=2;
}
else{
Ri=i;
R=j-1;
break;
}
}
else
a[i]=a[mi];
}
free(p);
return;
}
void init( int n ){
N = 1;
while( N < n ) N *= 2;
int i;
for( i = 1; i < N + n; i++ ) tree[i] = 0;
}
void range_increment( int i, int j, int val ){
for( i += N, j += N; i <= j; i = ( i + 1 ) / 2, j = ( j - 1 ) / 2 )
{
if( i % 2 == 1 ) tree[i] = max(tree[i],val);
if( j % 2 == 0 ) tree[j] = max(tree[j],val);
}
}
int query( int i ){
int ans = 0,j;
for( j = i + N; j; j /= 2 ) ans = max(ans,tree[j]);
return ans;
}
int max(int x,int y){
return (x>y)?x:y;
}
void update(int x,int y,int z){
if(z>NN){
int m=x+z/2;
if(z%2)
if(NN%2)
update(m-NN/2,m+NN/2,NN);
else
update(m-NN/2+1,m+NN/2-1,NN-1);
else
if(NN%2)
update(m-NN/2,m+NN/2-1,NN-1);
else
update(m-NN/2,m+NN/2-1,NN);
}
if(y<NN){
range_increment(0,x,z);
range_increment(y+1,NN-1,z);
}
else
range_increment(y-NN+1,x,z);
return;
}
void sort_a2(int*a,int*b,int size){
if (size < 2)
return;
int m = (size+1)/2,i;
int*left_a,*left_b,*right_a,*right_b;
left_a=(int*)malloc(m*sizeof(int));
right_a=(int*)malloc((size-m)*sizeof(int));
left_b=(int*)malloc(m*sizeof(int));
right_b=(int*)malloc((size-m)*sizeof(int));
for(i=0;i<m;i++){
left_a[i]=a[i];
left_b[i]=b[i];
}
for(i=0;i<size-m;i++){
right_a[i]=a[i+m];
right_b[i]=b[i+m];
}
sort_a2(left_a,left_b,m);
sort_a2(right_a,right_b,size-m);
merge2(a,left_a,right_a,b,left_b,right_b,m,size-m);
free(left_a);
free(right_a);
free(left_b);
free(right_b);
return;
}
void merge2(int*a,int*left_a,int*right_a,int*b,int*left_b,int*right_b,int left_size, int right_size){
int i = 0, j = 0;
while (i < left_size|| j < right_size) {
if (i == left_size) {
a[i+j] = right_a[j];
b[i+j] = right_b[j];
j++;
} else if (j == right_size) {
a[i+j] = left_a[i];
b[i+j] = left_b[i];
i++;
} else if (left_a[i] <= right_a[j]) {
a[i+j] = left_a[i];
b[i+j] = left_b[i];
i++;
} else {
a[i+j] = right_a[j];
b[i+j] = right_b[j];
j++;
}
}
return;
}
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