学步园

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. 

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.

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

5
Ab3bd

2

IOI 2000

没有啥要说的只有一个注意点。。。

d数组如果是int类型的一定会Memory Limit Exceeded

但是改成short int 就AC了

AC代码：

看到有的人使用滚动数组。。空间开销非常小，，，有机会试试

#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <math.h>
#include <sstream>
#include <vector>
#include <stack>
#include <map>
#include <queue>
#include <set>
#include <iostream>
#include <stdlib.h>
#include <cctype>
#define rep(i,s,e) for(int i = (s);i<(e);++i)
#define maxn 5001
#define INF 1000000000
#define eps 1e-6
using namespace std;
int n;
char A[maxn];
char B[maxn];
short int d[maxn][maxn];
int main()
{
    //freopen("in.txt","r",stdin);
    while(scanf("%d",&n)==1)
    {
       scanf("%s",A);
       memset(d,0,sizeof(d));
       for(int i  = n-1;i>=0;--i)
        B[i] = A[n - 1 - i];

       for(int i = 1;i<=n;++i)
        for(int j = 1;j<=n;++j)
        {
            if(A[i-1] == B[j - 1])
            d[i][j] = d[i - 1][j - 1] + 1;
            else
            d[i][j] = max(d[i-1][j],d[i][j-1]);
        }
        cout<<n - d[n][n]<<endl;
    }
    return 0;
}