[LeetCode 1290] Convert Binary Number in a Linked List to Integer

문제 바로가기

Description

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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

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

Example 2

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• Input: head = [0]
• Output: 0

Constraints

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

Hint

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Hint 1

  Traverse the linked list and store all values in a string or array. convert the values obtained to decimal value.
	

Hint 2

  You can solve the problem in O(1) memory using bits operation. use shift left operation ( << ) and or operation ( | ) to get the decimal value in one operation.
	

Code

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내 제출

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public int getDecimalValue(ListNode head) {
    int ans = 0;
    for (; head != null; head = head.next) {
        ans = ans << 1 | head.val;
    }
    return ans;
    }
}

Runtime	Memory
0 ms	41.4 MB

다른 풀이

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public int getDecimalValue(ListNode head) {
        StringBuilder sb = new StringBuilder();
        ListNode temp = head;
        while(temp != null){
            sb.append(temp.val);
            temp = temp.next;
        }

        return Integer.parseInt(sb.toString(), 2);
    }
}

Reference

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• https://github.com/doocs/leetcode/blob/main/solution/1200-1299/1290.Convert%20Binary%20Number%20in%20a%20Linked%20List%20to%20Integer/Solution.java