leetcode-5.4[191. 位1的個數、202. 快樂數、203. 移除鏈表元素]（python實現)

題目1

題解1

class Solution:
    def hammingWeight(self, n: int) -> int:
        sum = 0
        # 每次減去一個1，然後與原值相與，得到的值會少一個1
        while n != 0:
            sum += 1
            n &= (n-1)
        return sum

附上題目鏈接

題目2

題解2

def isHappy(self, n: int) -> bool:

    def get_next(n):
        total_sum = 0
        while n > 0:
            n, digit = divmod(n, 10)
            total_sum += digit ** 2
        return total_sum
    # 常見一個集合，用來證明是否進入死循環
    seen = set()
    while n != 1 and n not in seen:
        seen.add(n)
        n = get_next(n)
    return n == 1

附上題目鏈接

題目3

題解3

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def removeElements(self, head: ListNode, val: int) -> ListNode:
        """
            遍歷鏈表
        """
        # 常見一個虛假節點
        fakeNode = ListNode("inf")
        fakeNode.next = head
        p = fakeNode
        n = fakeNode.next
        
        while n:
            if n.val == val:
                p.next = p.next.next
            else:
                p = p.next
            n = n.next
        return fakeNode.next

    def removeElements(self, head: ListNode, val: int) -> ListNode:
        """
            遞歸法
        """
        if head is None: return
        head.next = self.removeElements(head.next, val)
        return head.next if head.val == val else head

附上題目來鏈接