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