本文共 2953 字,大约阅读时间需要 9 分钟。
class Solution(object): def checkRecord(self, s): """ :type s: str :rtype: bool """ countA = 0 for i in range(len(s)): if s[i]=='A': countA+=1 if countA>1: return False if i>1 and s[i]=='L' and s[i-1] == 'L' and s[i-2]=='L': return False return True
设dp[k][x][y] 为长度为k的有x个A和以y个L结尾的个数
dp[n][0][0] = sum(dp[n-1][0]) 即结尾增加一个P dp[n][0][1] = dp[n-1][0][0] 即结尾增加一个L dp[n][0][2] = dp[n-1][0][1] 即结尾增加一个L dp[n][1][0] = sum(dp[n-1][0]) + sum(dp[n-1][1])前者增加一个A后者增加一个P dp[n][1][1] = dp[n-1][1][0] 即结尾增加一个L dp[n][1][2] = dp[n-1][1][1] 即结尾增加一个L
由于dp[n] 只和dp[n-1]有关,所以可以采用滚动数组,该思路参考
class Solution(object): def checkRecord(self, n): """ :type n: int :rtype: int """ MOD = 1000000007 dp = [[1,1,0],[1,0,0]] for i in range(2,n+1): tmp = sum(dp[0]) % MOD dp[0][2] = dp[0][1] dp[0][1] = dp[0][0] dp[0][0] = tmp tmp = (dp[0][0] + sum(dp[1]))%MOD dp[1][2] = dp[1][1] dp[1][1] = dp[1][0] dp[1][0] = tmp return (sum(dp[0])+sum(dp[1]))%MOD
注意正负号和0的特殊处理
class Solution(object): def convertToBase7(self, num): """ :type num: int :rtype: str """ ret,flag = '',1 if num<0: flag = 0 num = -num while(num): ret = str(num % 7)+ret num = num/7 if ret == '': return '0' if flag: return ret else: return '-'+ret
能够扩展的条件是 单词连续个数大于3 先统计S中单词的个数 query 如heeellooo -> [(h,1),(e,3),(l,2),(o,3)] 对于每一个word来说,也统计word中单词的个数,candidate 如 hello -> [(h,1),(e,1),(l,2),(o,1)] 检查 len(query) == len(candidate) ? 检查 query[i][0] == candidate[i][0] ? 检查 query[i][1] >= candidate[i][1] 且如果> 成立的话 ,需要检查query[i][1]>=3 ?
class Solution(object): def expressiveWords(self, S, words): """ :type S: str :type words: List[str] :rtype: int """ def countLetters(word): cnt,last,ans = 0,'',[] for c in word: if c == last: cnt+=1 else: if cnt: ans.append((last,cnt)) cnt,last = 1,c if cnt: ans.append((last,cnt)) return ans def check(query,candidate): if len(query)!=len(candidate): return 0 for c,w in zip(query,candidate): if c[0] != w[0]: return 0 if c[1] < w[1]: return 0 if c[1] > w[1] and c[1]<3: return 0 return 1 query = countLetters(S) ans = 0 for word in words: candidate = countLetters(word) ans+=check(query,candidate) return ans
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