SCU - 4438（KMP)

#include 
#define LL long long
#define fread() freopen("in.in","r",stdin)
#define fwrite() freopen("out.out","w",stdout)
using namespace std;
#define maxn 5000040
string st;
string str;
string temp;
int nxt[maxn];

struct Node{
    char x;
    int j;
    Node(char x_,int j_){
        x = x_;
        j = j_;
    }
};
stackv;
void get_next()
{
    memset(nxt,0,sizeof(nxt));
    int i = 0 , j = -1 ;
    nxt[0] = -1;
    while( i < st.size() )
    {
        if( j == -1 || st[i] == st[j] )nxt[++i] = ++j;
        else j = nxt[j];
    }
}


void get_pos()
{
    int i = 0 , j = 0;
    while( i < str.size() )
    {
        if( j == -1 || str[i] == st[j] ){
            i++ , j++;
            v.push({str[i-1],j});
            if( j == st.size() )
            {
                int len = st.size();
                while(len--) v.pop();
                if(v.empty()) j = 0;
                    else j = v.top().j;
            }
        }
        else {
            j = nxt[j];
        }
    }
    int cnt = 0;
    temp = "";
    while(!v.empty()){
       temp += v.top().x;
        v.pop();
    }
    for(int i = temp.size()- 1; i >=0 ; --i)
        printf("%c",temp[i]);
    cout << endl;
}

int main()
{
    while( cin >> st >> str )
    {
        get_next();
        get_pos();
    }
}