package Algorithms.string;

public class IsNumber {

public boolean isNumber(String s) {

if (s == null) {

return false;

}

// cut the leading spaces and tail spaces.

String sCut = s.trim();

/*

Some examples:

"0" => true

" 0.1 " => true

"abc" => false

"1 a" => false

"2e10" => true

*/

int len = sCut.length();

boolean num = false;

boolean exp = false;

boolean dot = false;

for (int i = 0; i < len; i++) {

char c = sCut.charAt(i);

if (c == 'e') {

if (!num || exp) {

return false;

}

exp = true;

num = false; // Should be: 2e2 , so there should be number follow "e"

} else if (c <= '9' && c >= '0') {

num = true;

} else if (c == '.') {

if (exp || dot) { // can't be: e0.2 can't be: ..

return false;

}

dot = true;

} else if (c == '+' || c == '-') {

if (i != 0 && sCut.charAt(i - 1) != 'e') { // filter : " 005047e+6", this is true.

return false;

}

} else {

// invalid character.

return false;

}

}

return num;

}

}