c - designing a algorithm for a large data -

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i read 1 of question being asked job interview of software engineer.

if there 1000 websites , 1000 users, write program , data-structure such can query followin @ real time: 1. given user, list of sites he/she has visited 2. given website, list of users have visited it.

i think wanted sort of pseudo code or designing algorithm..

can guys give tips this?

one thing - in order able answer both queries, need store pairs mean user has visited given website. propose following:

you have structure:

struct visitpair{   int websiteid;   int userid;   visitpair* nextforuser;   visitpair* nextforwebsite; };

nextforuser point next pair given user or null if there no next pair given user, nextforwebsite point next pair website. user , website like:

struct user {   char* name;   visitpair* firstpair; };  struct website {   char* url;   visitpair* firstpair; };

i assume both website-s , users stored in arrays, these arrays websites , users. adding new visitpair relatively easy:

void addnewpair(int siteid, int userid) {   visitpair* newpair = (visitpair*)malloc(sizeof(vizitpair));   newpair->nextforuser = users[userid]->firstpair;   users[userid]->firstpair = newpair;   newpair->nextforwesite = websites[siteid]->firstpair;   websites[siteid]->firstpair = newpair; }

printing users website , websites user done iterating on list should able that.

in short create structure has 2 lists integrated. not think there can solution better complexity 1 has linear complexity respect answer , constant complexity adding pair.

hope helps.


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