0065. Valid Number
https://leetcode.com/problems/valid-number
Description
A valid number can be split up into these components (in order):
A decimal number or an integer.
(Optional) An
'e'
or'E'
, followed by an integer.
A decimal number can be split up into these components (in order):
(Optional) A sign character (either
'+'
or'-'
).One of the following formats:
One or more digits, followed by a dot
'.'
.One or more digits, followed by a dot
'.'
, followed by one or more digits.A dot
'.'
, followed by one or more digits.
An integer can be split up into these components (in order):
(Optional) A sign character (either
'+'
or'-'
).One or more digits.
For example, all the following are valid numbers: ["2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3", "3e+7", "+6e-1", "53.5e93", "-123.456e789"]
, while the following are not valid numbers: ["abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53"]
.
Given a string s
, return true
if s
is a valid number.
Example 1:
**Input:** s = "0"
**Output:** true
Example 2:
**Input:** s = "e"
**Output:** false
Example 3:
**Input:** s = "."
**Output:** false
Example 4:
**Input:** s = ".1"
**Output:** true
Constraints:
1 <= s.length <= 20
s
consists of only English letters (both uppercase and lowercase), digits (0-9
), plus'+'
, minus'-'
, or dot'.'
.
ac
The key is to understand the rules
class Solution {
public boolean isNumber(String s) {
// edge cases
if (s == null) return false;
s = s.trim();
if (s.length() == 0) return false;
boolean signSeen = false;
boolean dotSeen = false;
boolean eSeen = false;
boolean numberSeen = false;
int n = s.length();
for (int i = 0; i < n; i++) {
char c = s.charAt(i);
if (!isValid(c)) return false; // not a valid char
// sign: first, right after e/E, not last,twice
if (c == '+' || c == '-') {
if (i > 0 && (s.charAt(i-1) != 'e' && s.charAt(i-1) != 'E')
|| i == n - 1)
return false;
signSeen = true;
}
// dot: once, not after e, last with numberSeen
if (c == '.') {
if (dotSeen || eSeen || i == n - 1 && !numberSeen) return false;
dotSeen = true;
}
// e/E: after number, once, not last
if (c == 'e' || c == 'E') {
if (!numberSeen || eSeen || i == n - 1) return false;
eSeen = true;
}
// numbers
if (c >= '0' && c <= '9') {
numberSeen = true;
}
}
return true;
}
private boolean isValid(char c) {
if (c == '.' || c == '+' || c == '-' || c == 'e' || c == 'E' || c >= '0' && c <= '9')
return true;
return false;
}
}
/*
trim()
special char: . e +- number
signSeen, first, after e, not last
dotSeen, once, not last, not after e
eSeen, after number, once, not last
numberSeen
*/
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