2024-03-26 Daily Challenge

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

March LeetCoding Challenge 26

Description

First Missing Positive

Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums.

You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space.

 

Example 1:

Input: nums = [1,2,0]
Output: 3
Explanation: The numbers in the range [1,2] are all in the array.

Example 2:

Input: nums = [3,4,-1,1]
Output: 2
Explanation: 1 is in the array but 2 is missing.

Example 3:

Input: nums = [7,8,9,11,12]
Output: 1
Explanation: The smallest positive integer 1 is missing.

 

Constraints:

  • 1 <= nums.length <= 105
  • -231 <= nums[i] <= 231 - 1

Solution

class Solution {
public:
  int firstMissingPositive(vector<int>& nums) {
    int len = nums.size();
    for(auto &n : nums) {
      if(n < 1) n = INT_MAX;
    }
    for(auto n : nums) {
      n = abs(n);
      if(n > len) continue;
      if(nums[n - 1] > 0) nums[n - 1] = -nums[n - 1];
    }
    for(int i = 0; i < len; ++i) {
      if(nums[i] > 0) return i + 1;
    }
    return len + 1;
  }
};

// Accepted
// 173/173 cases passed (148 ms)
// Your runtime beats 76.92 % of cpp submissions
// Your memory usage beats 40.04 % of cpp submissions (83.1 MB)
Algorithm