Leetcode_65 Valid Number

忽然想起又有一周没写博客了,今天没做其它的,就做了一道题,就写写这道题吧。

题目:

Validate if a given string is numeric.

Some examples:
"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.

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:其实就是考虑各种边界条件,考虑清楚就行了。

边界条件:

数字能够有前置空格和后置空格,数字中间不能有空格;
对于’.’:最多仅仅可以出现1次,其前面能够没有数字,但后面一定要有数字;
对于’e’:最多仅仅可以出现1次,其前后都必须有数字。但后面一定是整数,即不能出现’.’;
对于’+’和’-‘:’e’的前后都最多可以出现1次,且一定要在数字最前面出现;
至于其它字符。只能是数字(0~9)。

代码(有点笨的方法实现的,debug了好久):

bool leetcode_65_isnumber(char a)
{
 if (a >= '0'&&a <= '9')
 {
 return true;
 }
 return false;
}


bool Leetcode_65::isNumber(string s)
{
 int dianflag = 0, dian_num_begin_flag = 0, dian_num_end_flag = 0; //.的标志位
 int eflag = 0, e_num_begin_flag = 0, e_num_end_flag = 0; //e的标志位
 int jia_flag = 0, jian_flag = 0; //加号和减号的标志位
 int shuzi_flag = 0, e_shuzi_flag = 0; //第一个标志位表示前面出现了空格再出现数字,第二个标志位表示先出现数字再出现空格
 int after_e_flag = 0;
 int length = s.size();
 for (int i = 0; i < length; ++i)
 {
 if (s[i] == '.')
 {
 if (dianflag == 1)
 {
 return false;
 }
 if (eflag == 1)
 {
 return false;
 }
 dianflag = 1;
 }
 else if (s[i] == 'e')
 {
 if (eflag == 1)
 {
 return false;
 }
 if (shuzi_flag == 0)
 {
 return false;
 }
 if (i == length - 1)
 {
 return false;
 }
 eflag = 1;
 }
 else if (s[i] == '+' || s[i] == '-')
 {
 if (dianflag == 1)
 {
 if (i >= 1 && s[i - 1] == 'e')
 {

 }
 else
 {
 return false;
 }
 }
 if (shuzi_flag == 0)
 {
 if (jia_flag == 1)
 {
 return false;
 }
 jia_flag = 1;
 continue;
 }
 else if (eflag == 1 && e_shuzi_flag == 0)
 {
 jia_flag = 1;
 continue;
 }
 else
 {
 return false;
 }
 }
 else if (s[i] == ' ')
 {
 if ((jia_flag == 1 || jian_flag == 1) && (shuzi_flag == 0))
 {
 return false;
 }
 if (shuzi_flag == 1 || dianflag == 1)
 {
 while (s[i] == ' ')
 {
 ++i;
 if (i == length)
 {
 if (shuzi_flag == 0)
 {
 return false;
 }
 if (eflag == 1 && e_shuzi_flag == 0)
 {
 return false;
 }
 return true;
 }
 }
 return false;
 }
 else
 {
 continue;
 }
 }
 else if (leetcode_65_isnumber(s[i]))
 {
 if (dianflag == 0)
 {
 dian_num_begin_flag = 1;
 }
 else
 {
 dian_num_end_flag = 1;
 }
 if (eflag == 0)
 {
 e_num_begin_flag = 1;
 }
 else
 {
 e_num_end_flag = 1;
 }
 if (eflag == 1)
 {
 e_shuzi_flag = 1;
 }
 else
 {
 shuzi_flag = 1;
 }
 }
 else
 {
 return false;
 }
 }
 if (shuzi_flag == 0)
 {
 return false;
 }
 if (eflag == 1 && e_shuzi_flag == 0)
 {
 return false;
 }
 return true;
}

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