Complexity OJ question

One ：

Solution 1 ：

  Every time you rotate a number , Each number in the number will move back once ;

So for k In terms of number, then move K*N The total number of times ; So the time complexity is O(N); Obviously not in line with the meaning of the question ;

Solution 2 ：

This method tries the double pointer method , This is also a common solution in arrays ;

For these multi process steps , Be sure to draw a multi process graphic process , Mark the subscript critical point of the array ;

Missing numbers ：

  For the XOR operator ： a^a = 0; 

                                      a^0 = a;

I was working on this problem at that time , Because I only know a set of formulas , Instead of thinking about the underlying principle of XOR ;

First , Give Way x = 0; Exclusive or of arrays with missing numbers , Then XOR the array without missing numbers , The last number , Is the missing number in the array ;