Leetcode -- First Missing Positive

 class Solution {  
 public:  
   int firstMissingPositive(int A[], int n) {  
     sort(A, A + n );  
     int num = 0;  
     for(int i = 0; i < n; ++i) {  
       if(A[i] > 0) {  
         if(num == A[i]) {  
           continue;  
         }  
         if(num + 1 != A[i] ) {  
           return num + 1;  
         } else {  
           num += 1;  
         }  
       }  
     }  
     return num + 1;  
   }  
 };