How to print elements of array of vectors of pairs? - c++

Question

I have an array of vector of pairs
vector <pair<int,int> > a[4]
.I have added elements to it using push_back.But I dont know how to print the elements.if i use an iteretor and print it like a[i].first or a[i].second it throws me error .Any other ways of doing it.Thanks in advance.
vector <pair<int,int> > a[4];
for(int i = 0;i < e;++i)
{
int x,y;
cin >> x >> y >> w;
a[x].push_back({w, y});
a[y].push_back({w, x});
}
This is how I push elements.But how to print them.
for(i=a[i].begin();i!=a[i].end();i++)
{
cout<<a[i].second<<" ";
}
I am getting the following error.I dnt know how to print them.
error: no match for 'operator[]' (operand types are 'std::vector<std::pair<int, int> >*' and 'std::vector<std::pair<int, int> >::iterator {aka __gnu_cxx::__normal_iterator<std::pair<int, int>*, std::vector<std::pair<int, int> > >}')
for(i=g[i].begin();i!=g[i].end();i++)

Answer 1

You did not provide any code so that we could be able to know what's going wrong at your machine.
But here is a working example on how to access a vector of pairs:
#include <utility>
#include <iostream>
#include <vector>
#include <string>
typedef std::pair<int, std::string> pairIntString;
int main()
{
std::vector<pairIntString> pairVec;
pairVec.push_back(std::make_pair(1, "One"));
pairVec.push_back(std::make_pair(2, "Two"));
pairVec.push_back(std::make_pair(3, "Three"));
for (std::vector<pairIntString>::const_iterator iter = pairVec.begin();
iter != pairVec.end();
++iter)
{
std::cout << "First: " << iter->first
<< ", Second: " << iter->second <<std::endl;
}
return 0;
}
Output, see here:
First: 1, Second: One
First: 2, Second: Two
First: 3, Second: Three
Edit #1:
Now you provide code, but you are actually using an array of vectors of pairs: vector <pair<int,int> > a[4];. Further you put an iterator from the begin() method into the [] operator. It seems that you mixed a lot of things e.g. here i=a[i].begin() (one i is iterator and another is an index) and don't understand what they really are for. Please look at my example and read about arrays and vectors and how to access them properly. Also read about the difference of indexed and iterator based access.
Edit #2:
This loop:
for(i=a[i].begin();i!=a[i].end();i++)
{
cout<<a[i].second<<" ";
}
should probably be:
/* loop through the fixed size array */
for(size_t idx = 0; idx < 4; ++i)
{
cout << "Array element idx: " << idx << endl;
/* get the iterator of the specific array element */
for (vector <pair<int,int> >::const_iterator iter = a[idx].begin();
iter != a[idx].end();
++iter)
{
cout << "First: " << iter->first
<< ", Second: " << iter->second << endl;
}
}
as you're having an array of vector of pairs you have two loop over the array and the vector. Because the array has a fixed size of 4 I used it as maximum.

Answer 2

vector <pair<int,int>> vec[5];
vector <pair<int,int>> :: iterator it;
for(int i=0;i<5;i++){
for(it=vec[i].begin(); it!=vec[i].end();it++) cout << it->first << " " << it->second << " -> ";
cout << "\n";
}

Answer 3

vector<pair<int,int>> v;
int n , in1 , in2;
cin >> n;
for(int i = 0 ; i < n ; i++)
{
cin >> in1 >> in2;
v.push_back(make_pair(in1,in2));
}
for(int i = 0 ; i < n ; i++)
cout << v[i].first << " " << v[i].second << endl;
return 0;

Answer 4

I used this concept in a question and you can check out the code which do the same what you wanted
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define loop(i, k, n) for(int i = k; k < n ? i < n : i >= n; k < n ? i+=1 : i-=1)
#define pll pair<ll, ll>
#define pb push_back
#define po pop_back
#define mp make_pair
#define F first
#define S second
#define endl "\n"
int main()
{
ll n, k;
cin >> n >> k;
ll arr[n];
ll ansArr[n] = {0};
vector <pair<ll, ll>> v[n];
loop(i, 0, n) cin >> arr[i];
loop(i, 0, n) {
if(arr[i] < 0) {
for(int j = i+1; j <= i+k && j < n; j++) {
if(arr[j] > 0) v[j].pb(mp(arr[i], i)); // Taking input in pairs
}
for(int j = i-1; j >= i-k && j >= 0; j--) {
if(arr[j] > 0) v[j].pb(mp(arr[i], i)); // Taking input in pairs
}
}
}
// Printing the result
loop(i, 0, n) {
for(auto it : v[i]) cout << it.F << " ";
cout << endl;
for(auto it : v[i]) cout << it.S << " ";
cout << endl;
}
return 0;
}