2021-10-06 Daily-Challenge

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In: DailyChallenge

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

October LeetCoding Challenge 6

Description

Find All Duplicates in an Array

Given an integer array nums of length n where all the integers of nums are in the range [1, n] and each integer appears once or twice, return an array of all the integers that appears twice.

You must write an algorithm that runs in O(n) time and uses only constant extra space.

Example 1:

Input: nums = [4,3,2,7,8,2,3,1]
Output: [2,3]

Example 2:

Input: nums = [1,1,2]
Output: [1]

Example 3:

Input: nums = [1]
Output: []

Constraints:

  • n == nums.length
  • 1 <= n <= 10^5
  • 1 <= nums[i] <= n
  • Each element in nums appears once or twice.

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  vector<int> findDuplicates(vector<int>& nums) {
    int len = nums.size();
    vector<int> answer;
    for(int i = 0; i < len; ++i) {
      int pos = nums[i] > 0 ? nums[i] - 1 : -1 - nums[i];
      cout << pos << endl;
      if(nums[pos] > 0) {
        nums[pos] = -nums[pos]; 
      } else {
        answer.push_back(pos + 1);
      }
    }
    return answer;
  }
};

// Accepted
// 28/28 cases passed (60 ms)
// Your runtime beats 53.68 % of cpp submissions
// Your memory usage beats 74.16 % of cpp submissions (33.5 MB)
Algorithm