First Missing Positive.java

  //http://blog.csdn.net/linhuanmars/article/details/20884585
  public int firstMissingPositive(int[] A) {
        if(A==null || A.length==0)  
            return 1; 
        for(int i=0;i<A.length;i++)  
        {  
            if(A[i]<=A.length && A[i]>0 && A[A[i]-1]!=A[i])  
            {  
                int temp = A[A[i]-1];  
                A[A[i]-1] = A[i];  
                A[i] = temp;  
                i--;  
            }  
        }  
        for(int i=0;i<A.length;i++)  
        {  
            if(A[i]!=i+1)  
                return i+1;  
        }  
        return A.length+1;  
    }