Flatten 2D Vector in C++

Suppose we have a 2D vector, we have to design and implement an iterator to flatten that 2d vector. There will be different methods as follows −

• next() − This will return the next element of the current element

• hasNext() − This will check whether next element is present or not

So, if the input is like [[1,2],[3],[4]] then if we call the functions as follows −

• iterator.next();

• iterator.next();

• iterator.next();

• iterator.hasNext();

• iterator.hasNext();

• iterator.next();

• iterator.hasNext();

then the output will be [1,2,3,true, true,4,false]

To solve this, we will follow these steps −

• Define one 2D array v

• Define initializer this will take one 2D array v,

• rowPointer := 0

• colPointer := 0

• n := size of v

• while (rowPointer < n and colPointer >= size of v[rowPointer]), do −

  • (increase rowPointer by 1)

• Define a function next()

• x := v[rowPointer, colPointer]

• (increase colPointer by 1)

• if colPointer is same as size of v[rowPointer], then −

  • colPointer := 0

  • (increase rowPointer by 1)

  • while (rowPointer < n and colPointer >= size of v[rowPointer]), do −

    • (increase rowPointer by 1)

• return x

• Define a function hasNext()

• return false when rowPointer is same as n

Example 

Let us see the following implementation to get better understanding −

 Live Demo

#include <bits/stdc++.h>
using namespace std;
class Vector2D {
public:
   int rowPointer, colPointer;
   int n;
   vector<vector<int< > v;
   Vector2D(vector<vector<int< >& v){
      this->v = v;
      rowPointer = 0;
      colPointer = 0;
      n = v.size();
      while (rowPointer < n && colPointer >= v[rowPointer].size()){
         rowPointer++;
      }
   }
   int next(){
      //cout << rowPointer << " " << colPointer << endl;
      int x = v[rowPointer][colPointer];
      colPointer++;
      if (colPointer == v[rowPointer].size()) {
         colPointer = 0;
         rowPointer++;
         while (rowPointer < n && colPointer >= v[rowPointer].size()) {
            rowPointer++;
         }
      }
      return x;
   }
   bool hasNext(){
      return !(rowPointer == n);
   }
};
main(){
   vector<vector<int<> v = {{1,2},{3},{4}};
   Vector2D ob(v);
   cout << (ob.next()) << endl;
   cout << (ob.next()) << endl;
   cout << (ob.next()) << endl;
   cout << (ob.hasNext()) << endl;
   cout << (ob.next()) << endl;
   cout << (ob.hasNext());
}

Input

ob.next()
ob.next()
ob.next()
ob.hasNext()
ob.next()
ob.hasNext()

Output

1
2
3
1
4
0