卡在七十分不动

代码如下↓↓↓↓

#include<iostream>
#include<cstring>
using namespace std;
string s1,s2;
short f[5001][5001];
int n;
int main(){
    getchar();
	getline(cin,s1);s1=' '+s1;
	s2=' ';
    n=s1.length();
	for (int i=n;i>=1;i--) s2+=s1[i];
	memset(f,0,sizeof(f));
	for (int i=1;i<=n;i++){
		for (int j=1;j<=n;j++){
			if (s1[i]==s2[j]){
				f[i][j]=f[i-1][j-1]+1;
			}else{
				if (f[i-1][j]>f[i][j-1]){
					f[i][j]=f[i-1][j];
				}else{
					f[i][j]=f[i][j-1];
				} 
			}
		}
	}
	
	printf("%d\n",n-f[n][n]);
	return 0;
}

给位大神求助