LeetCode（Linked List)1290. Convert Binary Number in a Linked List to Integer

Bertha 。 2023-09-24 21:07 20阅读 0赞

# 1.问题 #

Given head which is a reference node to a singly-linked list. The value of each node in the linked list is either 0 or 1. The linked list holds the binary representation of a number.

Return the decimal value of the number in the linked list.

The most significant bit is at the head of the linked list.

Example 1:

![在这里插入图片描述][7d00c7244a6947bb8b44deb39216b263.png]

> Input: head = \[1,0,1\]  
> Output: 5  
> Explanation: (101) in base 2 = (5) in base 10

Example 2:

> Input: head = \[0\]  
> Output: 0

Constraints:

*  The Linked List is not empty.
 *  Number of nodes will not exceed 30.
 *  Each node’s value is either 0 or 1.

# 2. 解题思路 #

## 方法1： ##

> 1.设定临时ListNode temp = head  
> 2.获得head的长度  
> 3.根据二进制转十进制是结点的值

## 方法2： ##

> (2\*n) + val方式求解

# 3. 代码 #

二进制转10进制方法  
![在这里插入图片描述][6a3a3168c94d4480bf9a77c9b6f509a9.png]

## 代码1： ##

class Solution {
        
        public int getDecimalValue(ListNode head) {
        
            ListNode temp = head;//1.设定临时ListNode temp = head
            int length=0;
            while(head!=null){
        //2.获得head的长度
                length++;
                head=head.next;
            }
            int result=0;
            int count =length-1;
            while(count>=0&&temp!=null){
        //3.根据二进制转十进制是结点的值*Math.pow(2,count)
                result  += (int) ((temp.val)*(Math.pow(2,count)));
                count--;
                temp=temp.next;
            }
            return result;
            
        }
    }

### 本地代码运行 ###

/**
     * @author: Amy
     * @create: 2023-02-28 21:09
     **/
    public class LinkedList {
        
        static ListNode head;
        ListNode pre;
        public static int getDecimalValue(ListNode head) {
        
            ListNode temp = head;
            int length=0;
            while(head!=null){
        
                length++;
                head=head.next;
    
            }
            int result=0;
            int count =length-1;
            while(count>=0&&temp!=null){
        
                result  += (int) ((temp.val)*(Math.pow(2,count)));
                count--;
                temp=temp.next;
            }
            return result;
        }
        public static void push(int new_data) {
        
            ListNode new_node = new ListNode(new_data);
            new_node.next = head;
            head = new_node;
        }
        public void print(){
        
            ListNode node = head;
            while(node!=null){
        
                System.out.print(node.val+" ");
                node = node.next;
            }
    
        }
        public static void main (String[]args){
        
            LinkedList list = new LinkedList();
            list.push(1);
            list.push(0);
            list.push(1);
    
            System.out.println("\nCreated Linked list is:");
            list.print();
            int result = list.getDecimalValue( head);
            System.out.println("\nresult:");
            System.out.println(result);
    
        }
        static class ListNode {
        
            int val;
            ListNode next;
            ListNode(int value){
        
                val = value;
                next=null;
            }
        }
    }

Created Linked list is:
    1 0 1 
    result:
    5

## 代码2： ##

Loop	Character	Operation	  Result
    1	    ‘1’	        1	          1
    2	    ‘0’	        (1x2) + 0	  2
    3	    ‘1’	        (2*2) + 1	  5

class Solution {
        
        public int getDecimalValue(ListNode head) {
        
            int ans = 0;
            while (head != null) {
        
                ans = ans * 2 + head.val;
                head = head.next;
            }
    
            return ans;
        }
    }

### 本地代码运行 ###

/**
     * @author: Amy
     * @create: 2023-02-28 21:09
     **/
    public class LinkedList {
        
        static ListNode head;
        ListNode pre;
        public static int getDecimalValue(ListNode head) {
        
            int ans = 0;
            while (head != null) {
        
                ans = ans * 2 + head.val;
                head = head.next;
            }
    
            return ans;
        }
        public static void push(int new_data) {
        
            ListNode new_node = new ListNode(new_data);
            new_node.next = head;
            head = new_node;
        }
        public void print(){
        
            ListNode node = head;
            while(node!=null){
        
                System.out.print(node.val+" ");
                node = node.next;
            }
    
        }
        public static void main (String[]args){
        
            LinkedList list = new LinkedList();
            list.push(1);
            list.push(0);
            list.push(1);
    
            System.out.println("\nCreated Linked list is:");
            list.print();
            int result = list.getDecimalValue( head);
            System.out.println("\nresult:");
            System.out.println(result);
    
        }
        static class ListNode {
        
            int val;
            ListNode next;
            ListNode(int value){
        
                val = value;
                next=null;
            }
        }
    }

Created Linked list is:
    1 0 1 
    result:
    5

[7d00c7244a6947bb8b44deb39216b263.png]: https://img-blog.csdnimg.cn/7d00c7244a6947bb8b44deb39216b263.png
[6a3a3168c94d4480bf9a77c9b6f509a9.png]: https://img-blog.csdnimg.cn/6a3a3168c94d4480bf9a77c9b6f509a9.png