[leetcode] 341. Flatten Nested List Iterator 解题报告

题目链接: https://leetcode.com/problems/flatten-nested-list-iterator/

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.

Example 1:
Given the list [[1,1],2,[1,1]],

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1].

Example 2:
Given the list [1,[4,[6]]],

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,4,6].

思路: 和上题一样, 可以先用一个DFS将所有的值都先存起来, 然后设置一个索引标记, 如果调用next就把数组的下一个返回, 如果调用hasNext就看index是否超出了数组的范围.

leetcode题目更新好快啊, 越来越多了.

代码如下: 

/**
 * // 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:
    void DFS(vector<NestedInteger> &nestedList)
    {
        for(auto val: nestedList)
        {
            if(val.isInteger())
                vec.push_back(val.getInteger());
            else DFS(val.getList());
        }
    }
    
    NestedIterator(vector<NestedInteger> &nestedList):index(0), vec() {
        DFS(nestedList);    
    }

    int next() {
        return vec[index++];
    }

    bool hasNext() {
        if(index < vec.size())
            return true;
        return false;
    }
private:
    int index;
    vector<int> vec;
};

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