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feat(positive): first missing positive cpp #498

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feat(positive): first missing positive cpp #498

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40 changes: 40 additions & 0 deletions C++/first-missing-positive.cpp
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Original file line number Diff line number Diff line change
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/*
Problem -
41. 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.

The Optimized Solution -
Time Complexity: O(N)
Space Complexity: O(1)

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

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


class Solution {
public:
int firstMissingPositive(vector<int>& nums) {
int n = nums.size();

for (int i = 0; i < n; i++) {
while (nums[i] >= 1 && nums[i] <= n && nums[i] != nums[nums[i] - 1]) {
swap(nums[i], nums[nums[i] - 1]);
}
}

for (int i = 0; i < n; i++) {
if (i + 1 != nums[i]) {
return i + 1;
}
}

return n + 1;
}
};
3 changes: 2 additions & 1 deletion README.md
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Expand Up @@ -122,7 +122,8 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
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| 122 | [Best Time to buy and sell Stock II](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii) | [Python](./Python/best-time-to-buy-and-sell-stock-ii.py) <br> [C++](./C++/Best-Time-to-Buy-and-Sell-Stock-II.cpp) | _O(N)_ | _O(1)_ | Medium | Stocks | |
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| 41 | [First Missing Positive](https://leetcode.com/problems/first-missing-positive/) | [C++](./C++/first-missing-positive.cpp) | _O(N)_ | _O(1)_ | Hard | Array | |
| 42 | [Trapping Rain Water](https://leetcode.com/problems/trapping-rain-water/) | [Python](./Python/trapping_rain.py) | _O(N^2)_ | _O(N)_ | Hard | Array | |
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| 1134 🔒 | [Armstrong Number](https://leetcode.com/problems/armstrong-number/) | [Java](./Java/Armstrong-Number.java) | _O(N)_ | _O(1)_ | Easy | | |
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