有效数字(按顺序)可以分成以下几个部分:
- 一个 小数 或者 整数
- (可选)一个
'e'
或'E'
,后面跟着一个 整数
小数(按顺序)可以分成以下几个部分:
- (可选)一个符号字符(
'+'
或'-'
) - 下述格式之一:
- 至少一位数字,后面跟着一个点
'.'
- 至少一位数字,后面跟着一个点
'.'
,后面再跟着至少一位数字 - 一个点
'.'
,后面跟着至少一位数字
- 至少一位数字,后面跟着一个点
整数(按顺序)可以分成以下几个部分:
- (可选)一个符号字符(
'+'
或'-'
) - 至少一位数字
部分有效数字列举如下:
["2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3", "3e+7", "+6e-1", "53.5e93", "-123.456e789"]
部分无效数字列举如下:
["abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53"]
给你一个字符串 s
,如果 s
是一个 有效数字 ,请返回 true
。
解法1:(官方答案)
确定有限状态自动机
#
# @lc app=leetcode.cn id=65 lang=python3
#
# [65] 有效数字
#
# @lc code=start
from enum import Enum
class Solution:
def isNumber(self, s: str) -> bool:
State = Enum("State", [
"STATE_INITIAL",
"STATE_INT_SIGN",
"STATE_INTEGER",
"STATE_POINT",
"STATE_POINT_WITHOUT_INT",
"STATE_FRACTION",
"STATE_EXP",
"STATE_EXP_SIGN",
"STATE_EXP_NUMBER",
"STATE_END"
])
Chartype = Enum("Chartype", [
"CHAR_NUMBER",
"CHAR_EXP",
"CHAR_POINT",
"CHAR_SIGN",
"CHAR_ILLEGAL"
])
def toChartype(ch: str) -> Chartype:
if ch.isdigit():
return Chartype.CHAR_NUMBER
elif ch.lower() == "e":
return Chartype.CHAR_EXP
elif ch == ".":
return Chartype.CHAR_POINT
elif ch == "+" or ch == "-":
return Chartype.CHAR_SIGN
else:
return Chartype.CHAR_ILLEGAL
transfer = {
State.STATE_INITIAL: {
Chartype.CHAR_NUMBER: State.STATE_INTEGER,
Chartype.CHAR_POINT: State.STATE_POINT_WITHOUT_INT,
Chartype.CHAR_SIGN: State.STATE_INT_SIGN
},
State.STATE_INT_SIGN: {
Chartype.CHAR_NUMBER: State.STATE_INTEGER,
Chartype.CHAR_POINT: State.STATE_POINT_WITHOUT_INT
},
State.STATE_INTEGER: {
Chartype.CHAR_NUMBER: State.STATE_INTEGER,
Chartype.CHAR_EXP: State.STATE_EXP,
Chartype.CHAR_POINT: State.STATE_POINT
},
State.STATE_POINT: {
Chartype.CHAR_NUMBER: State.STATE_FRACTION,
Chartype.CHAR_EXP: State.STATE_EXP
},
State.STATE_POINT_WITHOUT_INT: {
Chartype.CHAR_NUMBER: State.STATE_FRACTION
},
State.STATE_FRACTION: {
Chartype.CHAR_NUMBER: State.STATE_FRACTION,
Chartype.CHAR_EXP: State.STATE_EXP
},
State.STATE_EXP: {
Chartype.CHAR_NUMBER: State.STATE_EXP_NUMBER,
Chartype.CHAR_SIGN: State.STATE_EXP_SIGN
},
State.STATE_EXP_SIGN: {
Chartype.CHAR_NUMBER: State.STATE_EXP_NUMBER
},
State.STATE_EXP_NUMBER: {
Chartype.CHAR_NUMBER: State.STATE_EXP_NUMBER
},
}
st = State.STATE_INITIAL
for ch in s:
typ = toChartype(ch)
if typ not in transfer[st]:
return False
st = transfer[st][typ]
return st in [State.STATE_INTEGER, State.STATE_POINT, State.STATE_FRACTION, State.STATE_EXP_NUMBER, State.STATE_END]
# @lc code=end