First Missing Positive

class Solution {
public:
    int firstMissingPositive(vector<int>& nums) {
        int n = nums.size();
        for (int i = 0; i < n; ) {
            if (nums[i] >= 1 && nums[i] <= n && nums[nums[i] - 1] != nums[i]) {
                swap(nums[i], nums[nums[i] - 1]);
            } else {
                ++i;
            }
        }
        for (int i = 0; i < n; ++i) if (nums[i] != i + 1) return i + 1;
        return n + 1;
    }
};

func firstMissingPositive(nums []int) int {
    n := len(nums)
    for i := 0; i < n; {
        if nums[i] >= 1 && nums[i] <= n && nums[nums[i]-1] != nums[i] {
            nums[i], nums[nums[i]-1] = nums[nums[i]-1], nums[i]
        } else {
            i++
        }
    }
    for i := 0; i < n; i++ {
        if nums[i] != i+1 {
            return i + 1
        }
    }
    return n + 1
}

from typing import List

class Solution:
    def firstMissingPositive(self, nums: List[int]) -> int:
        n = len(nums)
        i = 0
        while i < n:
            if 1 <= nums[i] <= n and nums[nums[i] - 1] != nums[i]:
                j = nums[i] - 1
                nums[i], nums[j] = nums[j], nums[i]
            else:
                i += 1
        for i in range(n):
            if nums[i] != i + 1:
                return i + 1
        return n + 1

var firstMissingPositive = function(nums) {
    const n = nums.length;
    let i = 0;
    while (i < n) {
        if (nums[i] >= 1 && nums[i] <= n && nums[nums[i] - 1] !== nums[i]) {
            const j = nums[i] - 1;
            [nums[i], nums[j]] = [nums[j], nums[i]];
        } else {
            i++;
        }
    }
    for (let i = 0; i < n; i++) {
        if (nums[i] !== i + 1) return i + 1;
    }
    return n + 1;
};

class Solution {
    public int firstMissingPositive(int[] nums) {
        int n = nums.length;
        for (int i = 0; i < n; ) {
            if (nums[i] >= 1 && nums[i] <= n && nums[nums[i] - 1] != nums[i]) {
                int j = nums[i] - 1;
                int tmp = nums[i];
                nums[i] = nums[j];
                nums[j] = tmp;
            } else {
                i++;
            }
        }
        for (int i = 0; i < n; i++) {
            if (nums[i] != i + 1) return i + 1;
        }
        return n + 1;
    }
}

function firstMissingPositive(nums: number[]): number {
    const n = nums.length;
    let i = 0;
    while (i < n) {
        if (nums[i] >= 1 && nums[i] <= n && nums[nums[i] - 1] !== nums[i]) {
            const j = nums[i] - 1;
            [nums[i], nums[j]] = [nums[j], nums[i]];
        } else {
            i++;
        }
    }
    for (let k = 0; k < n; k++) {
        if (nums[k] !== k + 1) return k + 1;
    }
    return n + 1;
}