python leetcode 331-340

概述#331classSolution(object):defisValidSerialization(self,preorder):stack=[]fornodeinpreorder.split(','):stack.append(node)whilelen(stack)>=3andstack[-1]==stack[-2]=='#&#03

# 331class Solution(object):    def isValIDSerialization(self, preorder):        stack = []        for node in preorder.split(','):            stack.append(node)            while len(stack) >= 3 and stack[-1] == stack[-2] == '#' and stack[-3] != '#':                stack.pop(), stack.pop(), stack.pop()                stack.append('#')        return len(stack) == 1 and stack.pop() == '#'

# 332class Solution:    def findItinerary(self, tickets: List[List[str]]) -> List[str]:        from collections import defaultdict        graph = defaultdict(List)        res = []        for x , y in sorted(tickets)[::-1]:            graph[x].append(y)        def dfs(tmp):            while graph[tmp]:                dfs(graph[tmp].pop())            res.append(tmp)        dfs('JFK')        return res[::-1]

# 333class Solution:    def largestBSTSubtree(self, root: TreeNode) -> int:        def helper(root):            if not root:                return float('inf'), float('-inf'), 0            l_min, l_max, lv = helper(root.left)            r_min, r_max, rv = helper(root.right)            if l_max < root.val < r_min:                return min(l_min, root.val), max(root.val, r_max), 1 + lv + rv            return float('-inf'), float('inf'), max(lv, rv)        return helper(root)[2]

# 334class Solution:    def increasingTriplet(self, nums: List[int]) -> bool:        first , second = float('inf') , float('inf')        for num in nums:            if num > second:                return True            if first > num:                first = num            elif first < num < second:                second = num        return False

# 335class Solution:    def isSelfCrossing(self, x: List[int]) -> bool:        if len(x) < 3: return False        for i in range(3, len(x)):            if x[i] >= x[i-2] and x[i-1] <= x[i-3]: return True            if i >= 4 and x[i-1] == x[i-3] and x[i-4] + x[i] >= x[i-2]: return True            if i >= 5 and x[i-3] >= x[i-5] and x[i-2] >= x[i-4] and x[i-3] - x[i-5] <= x[i-1] <= x[i-3] and x[i] + x[i-4] >= x[i-2]: return True        return False 

# 336class Solution:    def palindromePairs(self, words: List[str]) -> List[List[int]]:        palIDStr = []        rev_words = {}        res = []        for IDx, word in enumerate(words):            rev_words[word[::-1]] = IDx            if word[::-1] == word[:]:                palIDStr.append(IDx)        for IDx , word in enumerate(words):            if word:                for i in range(len(word)):                    left , right = word[:i] , word[i:]                    if left == left[::-1] and right in rev_words and rev_words[right] != IDx:                        res.append([rev_words[right] , IDx])                    if right == right[::-1] and left in rev_words and rev_words[left] != IDx:                        res.append([IDx , rev_words[left]])            else:                for loc in palIDStr:                    if loc != IDx:                        res.append([IDx , loc])        return res

# 337class Solution:    def rob(self, root: TreeNode) -> int:        def helper(root):            if not root:                return 0, 0            left, prev1 = helper(root.left)            right, prev2 = helper(root.right)            return max(prev1 + prev2 + root.val, left + right), left + right        return helper(root)[0]

# 338class Solution:    def countBits(self, num: int) -> List[int]:        #res = []        #for i in range(num + 1):        #    res.append(str(bin(i)).count('1'))        #return res 自己做的        dp = [0] * (num + 1)        for i in range(1, num + 1):              dp[i] = dp[i // 2] + (i % 2)           return dp  #看不懂

# 340class Solution:    def lengthOfLongestSubstringKdistinct(self, s: str, k: int) -> int:        if len(s) == 0 or k == 0:            return 0        dic = {}        n = len(s)        r , l = 0 , 0        res = 0        while r < n:            dic[s[r]] = r            r += 1            if len(dic) <= k:                res = max(res , r - l)                 else:                min1 = min(dic.values())                del dic[s[min1]]                l = min1 + 1        return res

 

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