POJ2955 Brakets（区间dp）

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<vector>
#include<string>
#include<cstring>
#include<map>
#include<set>
using namespace std;
typedef long long ll;
const int N=1e5+10;
const int inf=0x3f3f3f3f;
int f[110][110];
int main(){
    string s;
    while(cin>>s){
        if(s=="end")
        break;
        int i,j;
        s=" "+s;
        memset(f,0,sizeof f);
        int len,l,r;
        for(i=1;i<=s.size()-1;i++){
            if(s[i]=='('&&s[i+1]==')'||(s[i]=='['&&s[i+1]==']'))
            f[i][i+1]=2;
        }
        for(len=3;len<=s.size();len++){
            for(l=1;l+len-1<=s.size();l++){
                r=l+len-1;
                if(s[l]=='('&&s[r]==')'||(s[l]=='['&&s[r]==']')){
                    f[l][r]=max(f[l][r],f[l+1][r-1]+2);
                }
                for(int k=l;k<r;k++){
                    f[l][r]=max(f[l][r],f[l][k]+f[k+1][r]);
                }
                
            }
        }
        cout<<f[1][s.size()]<<endl; 
    }
}