First Missing Positive at LeetCode

FirstMissingPositive.java

public class Solution {
    public int firstMissingPositive(int[] A) {
        int n = A.length;

        int i = 0;
        while(i<n){
            if(A[i] > 0 && A[i] <= n && A[i]-1 != i && A[A[i]-1] != A[i]){
                int temp = A[A[i]-1];
                A[A[i]-1] = A[i];
                A[i] = temp;
            }
            else 
                i++;
        }
        
        for(i = 0;i<n;i++){
            if(A[i] != i+1)
                return i+1;
        }
        
        return n+1;
    }
}