isNumber.go

/* https://leetcode.com/problems/valid-number/
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 0-9
Exponent - "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.
*/

package lstring

import "strings"

func isNumber(s string) bool {
	s = strings.TrimSpace(s)

	var sn, e, pt, ok bool

	for _, c := range s {
		switch c {
		case '.':
			if pt = !pt; !pt {
				return false
			}
			sn = true
		case '-', '+':
			if sn = !sn; !sn {
				return false
			}
		case 'e', 'E':
			if e = !e; !e || !ok {
				return false
			}
			sn, pt, ok = false, true, false
		case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
			sn, ok = true, true
		default:
			return false
		}
	}

	return ok
}