POJ 1159 Palindrome

好吧，在几天一直做水题，找找手感，过两天开刷难题。

#include<cstdio>
#include<string>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const int MAXN = 5010;
short int dp[2][MAXN];
int main(){
    int n;
    string s1, s2;
    while(~scanf("%d", &n)){
        cin >> s1;
        s2.reserve(n);
        for(int i = n-1;i >= 0;i --) s2[n-i-1] = s1[i];
        memset(dp, 0, sizeof dp);
        for(int i = 1;i <= n;i ++){
            for(int j = 1;j <= n;j ++){
                if(s1[i-1] == s2[j-1]) dp[i%2][j] = dp[(i-1)%2][j-1] + 1;
                else dp[i%2][j] = max(dp[i%2][j-1], dp[(i-1)%2][j]);
            }
        }
        printf("%d
", n-dp[n%2][n]);
    }
    return 0;
}