First Missing Positive LeetCode solution in C++

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