## Monday, August 7, 2017

### [Leetcode] Flatten 2D Vector, Solution

Implement an iterator to flatten a 2d vector.
For example,
Given 2d vector =
```[
[1,2],
[3],
[4,5,6]
]
```
By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: `[1,2,3,4,5,6]`.
As an added challenge, try to code it using only iterators in C++ or iterators in Java.

[Thoughts]

[Code]
``````1:  class Vector2D {
2:  public:
3:    vector<vector<int>> data;
4:    int x = 0;
5:    int y = 0;
6:    int total = 0;
7:    int visited = 0;
8:    Vector2D(vector<vector<int>>& vec2d) {
9:      data = vec2d;
10:      for(auto list : vec2d) {
11:        total += list.size();
12:      }
13:    }
14:
15:    int next() {
16:      while(data[x].size() == 0) {x++;}
17:
18:      int cur = data[x][y];
19:      if(y+1 == data[x].size()) {
20:        x = x+1;
21:        y = 0;
22:      } else {
23:        y++;
24:      }
25:      visited ++;
26:      return cur;
27:    }
28:
29:    bool hasNext() {
30:      if(visited < total) return true;
31:
32:      return false;
33:    }
34:  };
35:
36:  /**
37:   * Your Vector2D object will be instantiated and called as such:
38:   * Vector2D i(vec2d);
39:   * while (i.hasNext()) cout << i.next();
40:   */
``````

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johnpatrick said...

To flatten a 2D vector, you can use the cross product. The cross product of two vectors, A and B, is given by the equation A × B = (a x b) + (c x d) where a, b, c, and d are the components of the vectors A and B. This information is gathered by professional book writing service.

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