花花酱 LeetCode 2094. Finding 3-Digit Even Numbers

zxi — Sun, 05 Dec 2021 06:16:33 +0000

You are given an integer array digits, where each element is a digit. The array may contain duplicates.

You need to find all the unique integers that follow the given requirements:

The integer consists of the concatenation of three elements from digits in any arbitrary order.
The integer does not have leading zeros.
The integer is even.

For example, if the given digits were [1, 2, 3], integers 132 and 312 follow the requirements.

Return a sorted array of the unique integers.

Example 1:

Input: digits = [2,1,3,0]
Output: [102,120,130,132,210,230,302,310,312,320]
Explanation: 
All the possible integers that follow the requirements are in the output array. 
Notice that there are no odd integers or integers with leading zeros.

Example 2:

Input: digits = [2,2,8,8,2]
Output: [222,228,282,288,822,828,882]
Explanation: 
The same digit can be used as many times as it appears in digits. 
In this example, the digit 8 is used twice each time in 288, 828, and 882.

Example 3:

Input: digits = [3,7,5]
Output: []
Explanation: 
No even integers can be formed using the given digits.

Example 4:

Input: digits = [0,2,0,0]
Output: [200]
Explanation: 
The only valid integer that can be formed with three digits and no leading zeros is 200.

Example 5:

Input: digits = [0,0,0]
Output: []
Explanation: 
All the integers that can be formed have leading zeros. Thus, there are no valid integers.

Constraints:

3 <= digits.length <= 100
0 <= digits[i] <= 9

Solution: Enumerate all three digits even numbers

Check 100, 102, … 998. Use a hashtable to check whether all digits are covered by the given digits.

Time complexity: O(1000*lg(1000))
Space complexity: O(10)

C++

// Author: Huahua
class Solution {
public:
  vector findEvenNumbers(vector& digits) {
    vector counts(10);
    for (int d : digits) ++counts[d];
    vector ans;
    for (int x = 100; x < 1000; x += 2) {
      bool valid = true;
      vector c(10);
      for (int t = x; t > 0; t /= 10)
        valid &= (++c[t % 10] <= counts[t % 10]);           
      if (valid) ans.push_back(x);
    }
    return ans;
  }
};

The post 花花酱 LeetCode 2094. Finding 3-Digit Even Numbers appeared first on Huahua's Tech Road.

Python-Like enumerate() In C++17 – C++ Weekly EP1

zxi — Sun, 17 May 2020 21:34:20 +0000

C++

// Author: Huahua
#include 
#include 
#include 
#include 
#include 
using namespace std;

// Python-Like enumerate() In C++17
// http://reedbeta.com/blog/python-like-enumerate-in-cpp17/
template ())),
          typename = decltype(std::end(std::declval()))>
constexpr auto enumerate(T && iterable) {
  struct iterator {
    int i;
    TIter iter;
    bool operator != (const iterator & other) const { return iter != other.iter; }
    void operator ++ () { ++i; ++iter; }
    auto operator * () const { return std::tie(i, *iter); }
  };
  struct iterable_wrapper {
    T iterable;
    auto begin() { return iterator{ 0, std::begin(iterable) }; }
    auto end() { return iterator{ 0, std::end(iterable) }; }
  };
  // return iterable_wrapper{ iterable }; // this makes a copy if iterable is a rvalue.
  return iterable_wrapper{ std::forward(iterable) };  
}

struct A {
  int val;
  A(int val): val(val) { cout << "A(int)" << endl; }
  A(const A& a): val(a.val) { cout << "A(A&)" << endl; }
  A(A&& a): val(a.val) { cout << "A(A&&)" << endl; }    
};

int main(int argc, char** argv) {
  vector arr{1, 2, 4};  
  
  for (size_t i = 0; i < arr.size(); ++i)
    cout << i << " " << arr[i] << endl;

  size_t idx = 0;
  for (int v : arr)
    cout << idx++ << " " << v << endl;

  for (auto it = begin(arr); it != end(arr); ++it)
    cout << distance(begin(arr), it) << " " << *it << endl;
  

  for (const auto& [i, v] : enumerate(arr))
    cout << i << " " << v << endl;

  list lst{"hello", "world!"};  

  for (const auto& [i, v] : enumerate(lst))
    cout << i << " " << v << endl;

  for (const auto& [i, v] : enumerate(string("abcde")))
    cout << i << " " << v << endl;

  vector vec;
  vec.reserve(3);
  vec.emplace_back(1);
  vec.emplace_back(2);
  vec.emplace_back(4);

  for (const auto& [i, v] : enumerate(vec))
    cout << i << " " << v.val << endl;

  for (const auto& [i, v] : enumerate(vector{A(1), A(2), A(4)}))
    cout << i << " " << v.val << endl;

  return 0;
}

The post Python-Like enumerate() In C++17 – C++ Weekly EP1 appeared first on Huahua's Tech Road.

enumerate Archives - Huahua's Tech Road

花花酱 LeetCode 2094. Finding 3-Digit Even Numbers

Solution: Enumerate all three digits even numbers

C++

Python-Like enumerate() In C++17 – C++ Weekly EP1

C++