Implement an iterator to flatten a 2d vector.

For example,

Given 2d vector =

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]`

.**[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: */
```

## 7 comments:

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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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Nice post on the concerned subject of 2d vector. Your experience is great regarding vector tracing. Thank you very much...

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