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

September LeetCoding Challenge 19

Description

Find the Duplicate Number

Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive.

There is only one repeated number in nums, return this repeated number.

You must solve the problem without modifying the array nums and uses only constant extra space.

Example 1:

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

Example 2:

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

Constraints:

• 1 <= n <= 105
• nums.length == n + 1
• 1 <= nums[i] <= n
• All the integers in nums appear only once except for precisely one integer which appears two or more times.

Follow up:

• How can we prove that at least one duplicate number must exist in nums?
• Can you solve the problem in linear runtime complexity?

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  int findDuplicate(vector<int>& nums) {
    for(auto i : nums) {
      i = i > 0 ? i : -i;
      if(nums[i] < 0) return i;
      nums[i] = -nums[i];
    }
    return -1;
  }
};

// Accepted
// 58/58 cases passed (90 ms)
// Your runtime beats 98.15 % of cpp submissions
// Your memory usage beats 99.24 % of cpp submissions (61 MB)