341-flatten-nested-list-iterator.md

341. Flatten Nested List Iterator - 扁平化嵌套列表迭代器

给定一个嵌套的整型列表。设计一个迭代器，使其能够遍历这个整型列表中的所有整数。

列表中的项或者为一个整数，或者是另一个列表。

示例 1:

输入: [[1,1],2,[1,1]]
输出: [1,1,2,1,1]
解释: 通过重复调用 next 直到 hasNext 返回false，next 返回的元素的顺序应该是: [1,1,2,1,1]。

示例 2:

输入: [1,[4,[6]]]
输出: [1,4,6]
解释: 通过重复调用 next 直到 hasNext 返回false，next 返回的元素的顺序应该是: [1,4,6]。

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题目标签：Stack / Design

题目链接：LeetCode / LeetCode中国

题解

Language	Runtime	Memory
cpp	16 ms	1.9 MB

/**
 * // 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:
    vector<int> res;
    int pos = 0;

    void dfs(NestedInteger& ni) {
        if (ni.isInteger()) {
            res.push_back(ni.getInteger());
        } else {
            for (auto i : ni.getList()) {
                dfs(i);
            }
        }
    }

public:

    NestedIterator(vector<NestedInteger> &nestedList) {
        for (auto ni : nestedList) {
            dfs(ni);
        }
    }

    int next() {
        return res[pos++];
    }

    bool hasNext() {
        return pos < res.size();
    }
};
static auto _ = [](){ ios::sync_with_stdio(false); cin.tie(nullptr); return 0; }();

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