博文中会简要介绍Leetcode P0251题目分析及解题思路。
“Flatten 2D Vector”是一道比较简单的题目。题目要求对给定的所有向量执行展开操作，将所有向量元素“铺平“，并可以使用类似于迭代器的方式遍历。
Design an iterator to flatten a 2D vector. It should support the next and hasNext operations.
Implement the Vector2D class:
- Vector2D(int[][] vec) initializes the object with the 2D vector vec.
- next() returns the next element from the 2D vector and moves the pointer one step forward. You may assume that all the calls to next are valid.
- hasNext() returns true if there are still some elements in the vector, and false otherwise.
以下是Java的题解代码实现。
class Vector2D {
private int ptr = 0, end = 0;
private List<Integer> elements = new ArrayList<>();
public Vector2D(int[][] vec) {
for (int[] v: vec) {
for (int e: v) {
elements.add(e);
this.end += 1;
}
}
}
public int next() {
return elements.get(ptr++);
}
public boolean hasNext() {
return (ptr < end);
}
}
/**
* Your Vector2D object will be instantiated and called as such:
* Vector2D obj = new Vector2D(vec);
* int param_1 = obj.next();
* boolean param_2 = obj.hasNext();
*/
以下是C++的题解代码实现。
class Vector2D {
public:
Vector2D(vector<vector<int>>& vec) {
for (vector<int> v: vec) {
for (int e: v) {
_elems.push_back(e);
_end++;
}
}
}
int next() {
return _elems[_p++];
}
bool hasNext() {
return (_p < _end);
}
private:
vector<int> _elems;
int _p = 0, _end = 0;
};
/**
* Your Vector2D object will be instantiated and called as such:
* Vector2D* obj = new Vector2D(vec);
* int param_1 = obj->next();
* bool param_2 = obj->hasNext();
*/