POJ 1159 Palindrome

#include <iostream>
#include <string>
#include <cstring>
#include <algorithm>
using namespace std;
int dp[2][5005];
int main() {
string s1, s2;
int n;
while (cin >> n) {
cin >> s1;
s2 = s1;
reverse(s2.begin(), s2.end());
memset(dp, 0, sizeof(dp));
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= n; j++) {  //  notice the order
dp[i % 2][j] = dp[(i - 1) % 2][j] > dp[i % 2][j - 1] ? dp[(i - 1) % 2][j] : dp[i % 2][j - 1];
if (s1[i - 1] == s2[j - 1]) {
int temp = dp[(i - 1) % 2][j - 1] + 1;
dp[i % 2][j] = dp[i % 2][j] > temp ? dp[i % 2][j] : temp;
}
}
}
cout << n - dp[n % 2]
<< "\n";
}
return 0;
}