Palindrome (P1159)

这个题，要注意内在会超出， 所以要用两个数组进行交替进行计算。在这里学到了用指针就感觉可以比较快速地进行交换。

就是求公共子序列，但数组保存的数据最后一个不一定是最大的，所以一直要保持他的最大。

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<queue>
#include<vector>
#include<cmath>
#include<set>
#include<cstdlib>
#include<cstring>
#include<stack>
#include<string>

using namespace std;

//freopen("C://i.txt","r",stdin);

char s[11111];
int n;
char rs[11111];

int  a[10000],b[10000];

int main()
{
	freopen("C://i.txt","r",stdin);
	int i,j,k;
	
	int *one ,*two, *three;
	
	while (cin>>n)
	{
		cin>>s;
	//	cout<<s<<endl;
		strcpy(rs,s);
		reverse(rs,rs+n);
	//	cout<<rs<<endl;
		
		memset(a,0,sizeof(a));
		
		memset(b,0,sizeof(b));
		one=a;
		two=b;
		
		int big=0;
		for (i=1;i<=n;i++)
		{
			for (j=1;j<=n;j++)
			{
				 if (s[i-1]==rs[j-1])
				{
					two[j]=one[j-1]+1;
				}
				else
				{
					two[j]=max(two[j-1],one[j]);
				}
				big=max(big,two[j]);   //最后一个不一定是最大的， 
			}
			
				
			three=one;
			one=two;
			two=three;
			
		}
		cout<<n-big<<endl;
		
		
		
	}
	
} 

Palindrome

Time Limit: 3000MS		Memory Limit: 65536K
Total Submissions: 42874		Accepted: 14613

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

5
Ab3bd

Sample Output

2