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[5/8] 341. Flatten Nested List Iterator

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작성일 2022.05.07 18:18

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[LeetCode 시즌 3] 2022년 5월 8일 문제입니다.

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

341. Flatten Nested List Iterator

Medium

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You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it.

Implement the NestedIterator class:

NestedIterator(List<NestedInteger> nestedList) Initializes the iterator with the nested list nestedList.
int next() Returns the next integer in the nested list.
boolean hasNext() Returns true if there are still some integers in the nested list and false otherwise.

Your code will be tested with the following pseudocode:

initialize iterator with nestedList
res = []
while iterator.hasNext()
    append iterator.next() to the end of res
return res

If res matches the expected flattened list, then your code will be judged as correct.

Example 1:

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

Example 2:

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

Constraints:

1 <= nestedList.length <= 500
The values of the integers in the nested list is in the range [-106, 106].

#LeetCode, #LinkedIn, #Apple, #Facebook, #Airbnb, #Twitter, #Uber, #Amazon, #Salesforce, #Stack, #Tree, #Depth-First Search(DFS), #Design, #Queue, #Iterator

링크

https://leetcode.com/problems/flatten-nested-list-iterator/ 1431 회 연결

익명
작성일 2022.05.08 10:37

class NestedIterator {
public:
    NestedIterator(vector<NestedInteger> &nestedList) {
        auto build = [&](auto &self, vector<NestedInteger> &l) -> void{
          for(auto &n : l) {
              if (n.isInteger()) v.emplace_back(n.getInteger());
              else self(self, n.getList());
          }
        };
        build(build, nestedList);
        cur = v.begin();
    }
    
    int next() {
        return *cur++;
    }
    
    bool hasNext() {
        return !(cur == v.end());
        
    }
    vector<int> v;
    vector<int>::iterator cur;
};

익명
작성일 2022.05.08 16:22

C++
Runtime: 20 ms, faster than 51.39% of C++ online submissions for Flatten Nested List Iterator.
Memory Usage: 12.8 MB, less than 93.05% of C++ online submissions for Flatten Nested List Iterator.

class NestedIterator {
private:
    vector<int> arr;
    int idx;
    
    void unwrap(NestedInteger &ni) {
        if (ni.isInteger()) {
            arr.push_back(ni.getInteger());
        }
        else {
            for (auto &elem : ni.getList()) {
                unwrap(elem);
            }
        }
    }
    
public:
    NestedIterator(vector<NestedInteger> &nestedList) {
        idx = 0;
        for (auto &elem : nestedList) {
            unwrap(elem);
        }
    }
    
    int next() {
        return arr[idx++];
    }
    
    bool hasNext() {
        return idx < arr.size();
    }
};

익명
작성일 2022.05.09 16:21

Runtime: 97 ms
Memory Usage: 17.9 MB

class NestedIterator:
    def __init__(self, nestedList: [NestedInteger]):
        self.iterator = 0
        self.tempList = []
        self.nestedList = nestedList
        self.dfs_making_list(0, self.nestedList)
        
    def dfs_making_list(self, idx, lst):
        if idx < len(lst) and lst[idx]._integer != None:
            self.tempList.append(lst[idx]._integer)
            self.dfs_making_list(idx + 1, lst)
        elif idx >= len(lst):
            return
        else:
            self.dfs_making_list(0, lst[idx]._list)
            self.dfs_making_list(idx + 1, lst)
            
            
    
    def next(self) -> int:
        t = self.tempList[self.iterator]
        self.iterator += 1
        return t
    
    def hasNext(self) -> bool:
        if self.iterator < len(self.tempList):
            return True
        else:
            return False