无需存储任何东西.不需要哈希集.(额外的内存)，你可以随心所欲在数组中移动.但是，必须对数组进行排序.我们知道最最小值是 1

No need to store anything. No need for hashsets. (Extra memory), You can do it as you move through the array. However, The array has to be sorted. And we know the very most minimum value is 1

import java.util.Arrays;
class Solution {
    public int solution(int[] A) {
        Arrays.sort(A);     
        int min = 1; 
        /*
         for efficiency — no need to calculate or access the 
         array object’s length property per iteration 
        */
        int cap = A.length; 

        
        for (int i = 0; i < cap; i++){
            if(A[i] == min){
                min++;
            }
        /* 
           can add else if A[i] > min, break; 
           as suggested by punit
         */
        }   
        /*
          min = ( min <= 0 ) ? 1:min; 
          which means: if (min <= 0 ){
          min =1} else {min = min} 
          you can also do: 
          if min <1 for better efficiency/less jumps
         */
        return min;    
    }
}