Poj 1159 Palindrome

#include <iostream>
#include <stdio.h>
#include <string.h>

#define M 5010

using namespace std;

void reserve(char *a,char *b)
{
for(int i=0;i<strlen(a);i++)
{
b[strlen(a)-1-i] = a[i];
}
b[strlen(a)] = '\0';
}

void lcs(char *a,char *b,int c[][M])
{
int n = strlen(a);
for(int i=1;i<=n;i++)
{
for(int j =1;j<=n;j++)
{
if(a[i-1] == b[j-1])
{
c[i%2][j] = c[(i-1)%2][j-1] + 1;
}
else
{
c[i%2][j] = max(c[(i-1)%2][j],c[i%2][j-1]);
}
}
}

}

int main()
{
#ifndef ONLINE_JUDGE
freopen("in.txt","r",stdin);
#endif
int n;
char a[M],b[M];
int c[2][M];
memset(a,0,sizeof(a));
memset(b,0,sizeof(b));
memset(c,0,sizeof(c));

scanf("%d",&n);
scanf("%s",a);
reserve(a,b);
lcs(a,b,c);

printf("%d\n",n - c[n%2]
);

return 0;
}