程式語言 - LeetCode - C++ - 341. Flatten Nested List Iterator


題目：


解答： 

/**
 * // 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 {
private:
    stack<NestedInteger> st;

public:
    NestedIterator(vector<NestedInteger> &nestedList) {
        for (int i = nestedList.size() - 1; i >= 0; --i) {
            st.push(nestedList[i]);
        }
    }
    
    int next() {
        int ans = st.top().getInteger();
        st.pop();

        return ans;
    }
    
    bool hasNext() {
        while (!st.empty()) {
            NestedInteger cur = st.top();

            if (cur.isInteger()) {
                return true;
            }

            st.pop();
            auto& lst = cur.getList();
            for (int i = lst.size() - 1; i >= 0; --i) {
                st.push(lst[i]);
            }
        }

        return false;
    }
};

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