Missing number-looking for the missing digit

Requirement: Give an array of int, containing the number 0, 1, 2, ..., n, to find the missing number;

If the input is [0, 1, 2] returns 3

Input array nums = [0, 1, 2, 4]; should return 3

Input nums = [2, 0]; should return 1

Input nums = [1, 0]; should return 2

Method 1: First sort, then linear search

Elements are not necessarily arranged in order;

Sort the array first, and then search sequentially

Importjava.util.Arrays; Public classSolution { Public intMissingnumber (int[] nums)  {Arrays.sort (nums); Sort Firstintindex;  for(index = 0; index < nums.length; index + +)) {            if(index!=Nums[index]) {                returnindex; }        }        returnindex; }}

This method is relatively easy to think of, but the disadvantage is that the speed is too slow

Method 2: Xor method

There are no duplicate elements in the input array, which can be handled by different or unique features.

XOR: The difference is 1, the same is 0;

Any number that is different from or unchanged from 0, for example: A^0 = A;

Xor between multiple numbers, A^b^c = A^c^b = a^ (b^c)

1. Assume that the input array is [0, 1, 3] and should return 2

An array can be specified [0, 1, 2, 3], which contains the missing number X

The specified array is actually an array that satisfies the default criteria.

X does not exist, only occupies a position; places their elements in a bitwise XOR, i.e.

0, 1, x, 3

0, 1, 2, 3

0^1^2^3^0^1^3 = 0^0^1^1^3^3^2 = 0^2 = 2 Get result "2"

2. Assuming that the input array is [2, 0], use the array [0, 1, 2] to perform the following operations:

0^0^1^2^2 = 1 Get result "1"

3. Assuming that the input array is [0, 1, 2, 3], specify an array [0, 1, 2, 3] calculated using the method above

0^0^1^1^2^2^3^3 = 0 result error; should actually return 4

The array we use for the calculation can also be seen as the subscript for the input array, plus 1, which should be calculated using [0, 1, 2, 3, 4].

0, 1, 2, 3, X

0, 1, 2, 3, 4 results returned 4

Java code

 Public int missingnumber (int[] nums) {    ifnull | | nums.length = = 0) {         return 0;    }     int result = 0;      for (int i = 0; i < nums.length; i++) {        ^= nums[i];         ^= i;    }     return result ^ nums.length;}

The code implements the XOR operation described previously

Missing number-find the missing digit