Problem
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.
Solution
class Solution {
public boolean isNumber(String s) {
if (s == null || s.length() == 0) return false;
s = s.trim();
int len = s.length();
if (len == 0) return false;
int signCount = 0;
boolean hasE = false;
boolean hasNum = false;
boolean hasPoint = false;
for (int i = 0; i < len; i++) {
char ch = s.charAt(i);
if (ch >= '0' && ch <= '9') {
hasNum = true;
} else if (ch == 'e' || ch == 'E') {
if (hasE || !hasNum || i == len-1) return false;
hasE = true;
} else if (ch == '.') {
if (hasPoint || hasE) return false;
//0. is true
if (i == len-1 && !hasNum) return false;
hasPoint = true;
} else if (ch == '+' || ch == '-') {
//two signs at most; should not appear in the end
if (signCount == 2 || i == len-1) return false;
//sign appears in the middle but no E/e
if (i > 0 && !hasE) return false;
signCount++;
} else return false;
}
return true;
}
}
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