求助！

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1001;

string s;
int n, r;
int f[maxn][maxn];

int main(){
	cin >> s;
	n = s.size();
	
	for (int i=1; i<=n; i++) f[i][i] = 0;
	
	for (int k=1; k<n; k++){
		for (int l=1; l<=n-k; l++){
			r = l+k;
			if (s[l] == s[r]) f[l][r] = f[l+1][r-1];
			else f[l][r] = min(f[l+1][r], f[l][r-1]) + 1;
		}
	}
	
	cout << f[1][n];
	
	return 0;
}