leetcode/lcci/16.01.Swap Numbers

comments	difficulty	edit_url
true	Medium	https://github.com/doocs/leetcode/edit/main/lcci/16.01.Swap%20Numbers/README_EN.md

16.01. Swap Numbers

中文文档

Description

Write a function to swap a number in place (that is, without temporary vari­ ables).

Example:

Input: numbers = [1,2]

Output: [2,1]

Note:

• numbers.length == 2

Solutions

Solution 1: Bitwise Operation

We can use the XOR operation \oplus to implement the swap of two numbers.

The XOR operation has the following three properties:

• Any number XORed with 0 remains unchanged, i.e., a \oplus 0=a.
• Any number XORed with itself results in 0, i.e., a \oplus a=0.
• The XOR operation satisfies the commutative and associative laws, i.e., a \oplus b \oplus a=b \oplus a \oplus a=b \oplus (a \oplus a)=b \oplus 0=b.

Therefore, we can perform the following operations on two numbers a and b in the array numbers:

• a=a \oplus b, now a stores the XOR result of the two numbers;
• b=a \oplus b, now b stores the original value of a;
• a=a \oplus b, now a stores the original value of b;

In this way, we can swap two numbers without using a temporary variable.

The time complexity is O(1), and the space complexity is O(1).

Python3

class Solution:
    def swapNumbers(self, numbers: List[int]) -> List[int]:
        numbers[0] ^= numbers[1]
        numbers[1] ^= numbers[0]
        numbers[0] ^= numbers[1]
        return numbers

Java

class Solution {
    public int[] swapNumbers(int[] numbers) {
        numbers[0] ^= numbers[1];
        numbers[1] ^= numbers[0];
        numbers[0] ^= numbers[1];
        return numbers;
    }
}

C++

class Solution {
public:
    vector<int> swapNumbers(vector<int>& numbers) {
        numbers[0] ^= numbers[1];
        numbers[1] ^= numbers[0];
        numbers[0] ^= numbers[1];
        return numbers;
    }
};

Go

func swapNumbers(numbers []int) []int {
	numbers[0] ^= numbers[1]
	numbers[1] ^= numbers[0]
	numbers[0] ^= numbers[1]
	return numbers
}

TypeScript

function swapNumbers(numbers: number[]): number[] {
    numbers[0] ^= numbers[1];
    numbers[1] ^= numbers[0];
    numbers[0] ^= numbers[1];
    return numbers;
}

Swift

class Solution {
    func swapNumbers(_ numbers: [Int]) -> [Int] {
        var numbers = numbers
        numbers[0] ^= numbers[1]
        numbers[1] ^= numbers[0]
        numbers[0] ^= numbers[1]
        return numbers
    }
}