[leetcode]341. Flatten Nested List Iterator

Analysis

週一鴨—— [每天刷題並不難0.0]

Given a nested list of integers, implement an iterator to flatten it.
Each element is either an integer, or a list – whose elements may also be integers or other lists.

用迭代的方法實現遞迴，所以用棧

Implement

/**
 * // This is
 
 the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * class NestedInteger {
 *   public:
 *     // Return true if this NestedInteger holds a single integer, rather than a nested list.
 *     bool isInteger() const;
 *
 *     // Return the single integer that this NestedInteger holds,
 
 if it holds a single integer
 *     // The result is undefined if this NestedInteger holds a nested list
 *     int getInteger() const;
 *
 *     // Return the nested list that this NestedInteger holds, if it holds a nested list
 *     // The result is undefined if this NestedInteger holds a single integer
 *
 
     const vector<NestedInteger> &getList() const;
 * };
 */
class NestedIterator {
public:
    NestedIterator(vector<NestedInteger> &nestedList) {
        for(int i=nestedList.size()-1; i>=0; i--)
            s.push(nestedList[i]);
    }

    int next() {
        NestedInteger tmp = s.top();
        s.pop();
        return tmp.getInteger();
    }

    bool hasNext() {
        while(!s.empty()){
            NestedInteger tmp = s.top();
            if(tmp.isInteger())
                return true;
            s.pop();
            for(int i=tmp.getList().size()-1; i>=0; i--)
                s.push(tmp.getList()[i]);
        }
        return false;
    }
private:
    stack<NestedInteger> s;
};

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