Validate if a given string can be interpreted as a decimal number.
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
0-9- Exponent -
e- Positive/negative sign -
+/-- Decimal point -
.
Of course, the context of these characters also matters in the input.
Example
"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
Thoughts
- 要注意考虑所有可能的
invalid的情况： - 对于正负号
+/-- 首个字符可以是正负号
- 指数后的首个字符可以是正负号
- 其他位置则不可以出现正负号
- 对于小数点
.：- 小数点只能出现一次
- 小数点前或者后要有数字出现
- 对于指数
e：- 指数只能出现一次
- 指数前必须有数字
- 指数后不能出现小数点
Code(JAVA)
public boolean isNumber(String s) {
s = s.trim();
boolean decimalShown = false;
boolean exponentShown = false;
boolean numberShown = false;
for(int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if(c >= '0' && c <= '9')
numberShown = true;
else if(c == '-' || c == '+') {
if(i != 0 && s.charAt(i-1) != 'e')
return false;
}
else if(c == '.' && !decimalShown)
decimalShown = true;
else if(c == 'e' && !exponentShown) {
if(!numberShown)
return false;
exponentShown = true;
decimalShown = true;
numberShown = false;
}
else
return false;
}
return numberShown;
}
