[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].

Follow up:
As an added challenge, try to code it using only iterators in C++ or iterators in Java.

[Thoughts]
实现题，按层从左到右遍历。

[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:   */