Today I have done leetcode's October LeetCoding Challenge with cpp.

October LeetCoding Challenge 20

Description

Flatten Nested List Iterator

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].

Solution

class NestedIterator {
  vector<int> integers;
  int len;
  int i;
  void solve(NestedInteger &nestedInt) {
    if(nestedInt.isInteger()) {
      integers.push_back(nestedInt.getInteger());
      return;
    }
    for(auto &l : nestedInt.getList()) {
      solve(l);
    }
  }
public:
  NestedIterator(vector<NestedInteger> &nestedList) {
    for(auto &nestedInt : nestedList) solve(nestedInt);
    len = integers.size();
    i = 0;
  }

  int next() {
    return integers[i++];
  }

  bool hasNext() {
    return i != len;
  }
};

// Accepted
// 43/43 cases passed (14 ms)
// Your runtime beats 84.39 % of cpp submissions
// Your memory usage beats 56.47 % of cpp submissions (13.1 MB)