回文樹(統計所有回文串的個數) - MCCME 1750 ПодпалиндромыПодпалиндромы Problem's Link: http://informatics.mccme.ru//mod/statements/view.php?chapterid=1750#

Mean: 

給你一個長度不超過1e5的字元串，要統計總共有多少個回文串。(第一次刷俄語題，還好有google翻譯)。

analyse:

如果題目說是不同回文串的話，這題就是一個裸的回文樹。

由于要求所有子串的回文數，是以我們在插入的時候還需要使用suffixLink往上走統計答案。

Time complexity: O(N)

Source code: 

/*

* this code is made by crazyacking

* Verdict: Accepted

* Submission Date: 2015-08-17-19.13

* Time: 0MS

* Memory: 137KB

*/

#include <queue>

#include <cstdio>

#include <set>

#include <string>

#include <stack>

#include <cmath>

#include <climits>

#include <map>

#include <cstdlib>

#include <iostream>

#include <vector>

#include <algorithm>

#include <cstring>

#define  LL long long

#define  ULL unsigned long long

using namespace std;

const int MAXN = 105000;

struct node

{

     int next[26];

     int len;

     int sufflink;

     int num;

};

int len;

char s[MAXN];

node tree[MAXN];

int num; // node 1 - root with len -1, node 2 - root with len 0

int suff; // max suffix palindrome

long long ans;

bool addLetter(int pos)

     int cur = suff, curlen = 0;

     int let = s[pos] - 'a';

     while(true)

     {

           curlen = tree[cur].len;

           if(pos-1-curlen>=0&&s[pos-1-curlen]==s[pos]) break;

           cur = tree[cur].sufflink;

     }

     if(tree[cur].next[let])

           suff = tree[cur].next[let];

           return false;

     } suff = ++num;

     tree[num].len = tree[cur].len + 2;

     tree[cur].next[let] = num;

     if(tree[num].len == 1)

           tree[num].sufflink = 2;

           tree[num].num = 1;

           return true;

           if(pos - 1 - curlen >= 0 && s[pos - 1 - curlen] == s[pos])

           {

                 tree[num].sufflink = tree[cur].next[let];

                 break;

           }

     tree[num].num = 1 + tree[tree[num].sufflink].num;

     return true;

}

void initTree()

     num = 2; suff = 2;

     tree[1].len = -1; tree[1].sufflink = 1;

     tree[2].len = 0; tree[2].sufflink = 1;

int main()

     gets(s);

     initTree();

     for(int i = 0;s[i]; i++)

           addLetter(i);

           ans += tree[suff].num;

     } cout << ans << endl;

     return 0;