[leetcode] 65. Valid Number

[leetcode] 65. Valid Number

Description

Validate if a given string can be interpreted as a decimal number.

Some examples:

"0" => true" 0.1 " => true"abc" => false"1 a" => false"2e10" => true" -90e3 " => true" 1e" => false"e3" => false" 6e-1" => true" 99e2.5 " => false"53.5e93" => true" --6 " => false"-+3" => false"95a54e53" => false

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one. However, here is a list of characters that can be in a valid decimal number:

Numbers 0-9Exponent - “e”Positive/negative sign - “+”/"-"Decimal point - “.”Of course, the context of these characters also matters in the input.

Update (2015-02-10): The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button to reset your code definition.

分析

题目的意思是：给定一个字符串，然后判断字符串是否是合法的数字。

leetcode上的hard类型的题目。这道题看似简单，但是没有找到方法却很难做，我参考了leetcode的解法，用.和e E等把字符串分为两部分，然后分开来判断其子字符串是否是数字，如果都是数字并且已经遍历到末尾了，就可以认为这个字符串是合法的。

代码

class Solution {public: bool isNumber(string s) { if(s.empty()){ return false; } int i=0; while(s[i]==' '){ i++; } bool numeric=scanInteger(s,i); if(s[i]=='.'){ i++; numeric=numeric|scanUnsignedInteger(s,i); } if(s[i]=='e'||s[i]=='E'){ i++; numeric=numeric&scanInteger(s,i); } while(s[i]==' '){ i++; } return numeric&&s[i]=='\0'; } bool scanInteger(string s,int& i){ if(s[i]=='+'||s[i]=='-'){ i++; } return scanUnsignedInteger(s,i); } bool scanUnsignedInteger(string s,int& i){ int t=i; while(s[t]>='0'&&s[t]<='9'){ t++; } bool flag=t>i; i=t; return flag; }};

参考文献

​​[编程题]valid-number​​

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