題目

https://leetcode-cn.com/problems/number-complement/

---

思路

我們想要返回已知數字的補數（num>=1）。

思路：

獲取 num 的二進制數

將 num 的二進制數取反

由于取反后，所有高位的 0 都會變為1，所以需要截取有效的低位，得到真正的返回結果

* 參考：How to extract ‘k’ bits from a given position in a number

https://www.geeksforgeeks.org/extract-k-bits-given-position-number/

How to extract ‘k’ bits from a given position ‘p’ in a number?

Examples:

Input : number = 171k = 5 p = 2 Output : The extracted number is 21 171 is represented as 0101011 in binary, so, you should get only 10101 i.e. 21. （從第2位開始，向左取5位）Input : number = 72k = 5 p = 1 Output : The extracted number is 8 72 is represented as 1001000 in binary, so, you should get only 01000 i.e 8.

Right shift number by p-1.

Do bit wise AND of k set bits with the modified number. We can get k set bits by doing (1 << k) – 1.

Example:

// Java program to extract k bits from a given // position.class GFG {// Function to extract k bits from p position// and returns the extracted value as integerstatic int bitExtracted(int number, int k, int p){return (((1 << k) - 1) & (number >> (p - 1)));}// Driver codepublic static void main (String[] args) {int number = 171, k = 5, p = 2;System.out.println("The extracted number is "+bitExtracted(number, k, p));} }

Output:

The extracted number is 21

---

代碼

1、易懂版

public class Solution {/*** 給你一個正整數 num ，輸出它的補數。補數是對該數的二進制表示取反。*/public static int findComplement(int num) {int bitLen = Integer.toBinaryString(num).length();return bitExtracted(~num, bitLen, 1);}// Function to extract k bits from p position// and returns the extracted value as integerstatic int bitExtracted(int number, int leftIndex, int rightIndex) {System.out.println(Integer.toBinaryString(number));int i = ((1 << leftIndex) - 1) & (number >> (rightIndex - 1));System.out.println(Integer.toBinaryString(i));return i;} }

2、簡化版

class Solution {public int findComplement(int num) {int bitLen=Integer.toBinaryString(num).length();return ((1 << bitLen) - 1) & ~num;} }

總結

以上是生活随笔為你收集整理的leetcode 476. 数字的补数（Java版）| How to extract ‘k’ bits from a given position in a number的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。