poj 1159(回文串dp)

Palindrome

Time Limit: 3000MS Memory Limit: 65536KTotal Submissions: 49315 Accepted: 16937

Description

A palindrome is a symmetrical string, that is, a string read identically from left to right as well as from right to left. You are to write a program which, given a string, determines the minimal number of characters to be inserted into the string in order to obtain a palindrome. 

As an example, by inserting 2 characters, the string "Ab3bd" can be transformed into a palindrome ("dAb3bAd" or "Adb3bdA"). However, inserting fewer than 2 characters does not produce a palindrome. 

Input

Your program is to read from standard input. The first line contains one integer: the length of the input string N, 3 <= N <= 5000. The second line contains one string with length N. The string is formed from uppercase letters from 'A' to 'Z', lowercase letters from 'a' to 'z' and digits from '0' to '9'. Uppercase and lowercase letters are to be considered distinct.

Output

Your program is to write to standard output. The first line contains one integer, which is the desired minimal number.

Sample Input

5Ab3bd

Sample Output

2

Source

IOI 2000

 

题目很简单。

事实上回文串能用到的唯一性质就是，若str[i] ~ str[j] 是回文串， 则str[i+1] ~ str[j-1] 也是回文串。

好好这个性质可以解决大多数的回文串题目。

 

贡献了一次Timeout， 很久没看到了。

 

提交记录：

1、Timeout，是因为脑残多写了一层循环。注意斜着填表的时候，当i和interval确定的时候，j就是唯一确定的，不要再对j进行循环！

2、Accepted。

 

代码如下：