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Flatten 2D Vector

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Description

https://leetcode.com/problems/flatten-2d-vector/

Solution

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class Vector2D {
private:
    vector<vector<int>> vec;
    vector<vector<int>>::iterator rowIter;
    vector<int>::iterator columnIter;
public:
    Vector2D(vector<vector<int>>& vec2d) {
        vec = vec2d;
        rowIter = vec.begin();
        while (rowIter != vec.end() && rowIter->size() == 0) ++rowIter;
        if (rowIter != vec.end()) columnIter = rowIter->begin();
    }

    int next() {
        int ret = *columnIter;
        ++columnIter;
        if (columnIter == rowIter->end()) {
            ++rowIter;
            while (rowIter != vec.end() && rowIter->size() == 0) ++rowIter;
            if (rowIter != vec.end()) columnIter = rowIter->begin();
        }
        return ret;
    }

    bool hasNext() {
        if (rowIter == vec.end()) return false;
        return true;
    }
};

/**
 * Your Vector2D object will be instantiated and called as such:
 * Vector2D i(vec2d);
 * while (i.hasNext()) cout << i.next();
 */