Untitled

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