.py.go 刷L站 19 20

py

class Solution:
    def removeNthFromEnd(self, head: Optional[ListNode], n: int) -> Optional[ListNode]:
        if head.next is None:
            return None

        fast_point = head

        while 0 < n and fast_point.next is not None:
            fast_point = fast_point.next
            n -= 1

        if n != 0:
            return head.next
        slow_point = head

        while fast_point.next is not None:
            fast_point = fast_point.next
            slow_point = slow_point.next

        slow_point.next = slow_point.next.next
        return head

如果n先小於零就是尺太短刪減某個元數至少要前後的next做連接，當尺太短就要自講想辦法刪除第一個或將倒數第二個接上nil。

也可以先遍歷一次求長度，本次使用快慢指針法。如圖就不多解釋了。

go

func removeNthFromEnd(head *ListNode, n int) *ListNode {
    if head.Next == nil {
        return nil 
    }
	fastPoint := head
	for ; 0 < n && fastPoint.Next != nil; n-- {
		fastPoint = fastPoint.Next
	}
	
	if n != 0 {
		return head.Next
	}
	slowPoint := head

	for fastPoint.Next != nil {
		fastPoint = fastPoint.Next
		slowPoint = slowPoint.Next
	}
	slowPoint.Next = slowPoint.Next.Next

	return head
}

線索太少，而且我英文不好。我已經想到兩種例外了。

一、"({)}" 
二、"({})"

直接用console的Testcase看看。

恩。大致上釐清了。他只看前一個有沒有對起來。如果他是要找匹配的就比較麻煩了。這樣就要寫更多判斷式來解題。但不管他要哪種。這種類型我都會用stack下去解題。

py

class Solution:
    def isValid(self, s: str) -> bool:
        token_stack = []
        for token in s:
            if token == "{" or token == "(" or token == "[":
                token_stack.append(token)
            elif not token_stack:
                return False
            else:
                if token == "}" and token_stack.pop() != "{":
                    return False
                if token == "]" and token_stack.pop() != "[":
                    return False
                if token == ")" and token_stack.pop() != "(":
                    return False

        if token_stack:
            return False
        else:
            return True

go

func isValid(s string) bool {
	var tokenStack []int32

	for _, token := range s {
		if token == 123 || token == 91 || token == 40 {
			tokenStack = append(tokenStack, token)
        } else if len(tokenStack) == 0 {
			return false
		} else {
			if tokenStack[len(tokenStack)-1] == 40 && token != 41 {
				return false
			}
			if tokenStack[len(tokenStack)-1] == 91 && token != 93 {
				return false
			}
			if tokenStack[len(tokenStack)-1] == 123 && token != 125 {
				return false
			}
			tokenStack = tokenStack[:len(tokenStack)-1]
		}
	}
	if len(tokenStack) == 0 {
		return true
	} else {
		return false
	}
}

以上，自己看吧，歡迎留言交流。