if(ist== NULL i=0){∥插在表前 newnode→hink= first; if (first ==NULL) last =newnode; first= newnode, ese /插在表中或末尾 newnode-link=p-link; if(p-link== NULL last newnode; p→link= newnode; return 1if ( first == NULL || i == 0 ) { //插在表前 newnode→link = first; if ( first == NULL ) last = newnode; first = newnode; } else { //插在表中或末尾 newnode→link = p→link; if ( p→link == NULL ) last = newnode; p→link = newnode; } return 1; }