# 65 Valid Number

### Problem

Validate if a given string is numeric.

Some examples: "0" => true " 0.1 " => true "abc" => false "1 a" => false "2e10" => true Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.

### Solutions

``````public class Solution {
public boolean isNumber(String s) {
s = s.trim();
if (s.indexOf("e") != -1) {
int cut = s.indexOf("e");
return validNumber(s.substring(0, cut), true) && validNumber(s.substring(cut + 1), false);
}
else {
return validNumber(s, true);
}
}
private boolean validNumber(String s, boolean canBeDouble) {
if (s.length() == 0) {
return false;
}
if (s.charAt(0) == '-' || s.charAt(0) == '+') {
s = s.substring(1);
}
if (s.indexOf(".") != -1) {
if (canBeDouble == false) {
return false;
}
int cut = s.indexOf(".");
return (validInteger(s.substring(0, cut), true) && validInteger(s.substring(cut + 1), false)) || (validInteger(s.substring(0, cut), false) && validInteger(s.substring(cut + 1), true));
}
else {
return validInteger(s, false);
}
}
private boolean validInteger(String s, boolean canBeEmpty) {
if (!canBeEmpty && s.length() == 0) {
return false;
}
for (int i = 0; i < s.length(); i ++) {
char c = s.charAt(i);
if (c < '0' || c > '9') {
return false;
}
}
return true;
}
}
``````
``````class Solution {
public boolean isNumber(String s) {
s = s.trim();
int cut = s.indexOf("e");
if (cut != -1) {
return isRealNumber(s.substring(0, cut), true) && isRealNumber(s.substring(cut + 1), false);
}
else {
return isRealNumber(s, true);
}
}

// assume 0001 is valid
private boolean isRealNumber(String s, boolean canBeDouble) {
if (s.length() > 0 && (s.charAt(0) == '-' || s.charAt(0) == '+')) {
s = s.substring(1);
}
int cut = s.indexOf(".");
if ( cut != -1) {
if (canBeDouble == false) {
return false;
}
return (isPureNumber(s.substring(0, cut), true) && isPureNumber(s.substring(cut + 1), false)) || (isPureNumber(s.substring(0, cut), false) && isPureNumber(s.substring(cut + 1), true));
}
else {
return isPureNumber(s, false);
}
}
private boolean isPureNumber(String s, boolean canBeEmpty) {
if (canBeEmpty == false && s.length() == 0) {
return false;
}
for (int i = 0; i < s.length(); i ++) {
char c = s.charAt(i);
if (c < '0' || c > '9') {
return false;
}
}
return true;
}
}
``````
``````class Solution {
public boolean isNumber(String s) {
s = s.trim();
int cut = s.indexOf("e");
if (cut != - 1) {
return isRational(s.substring(0, cut)) && isInteger(s.substring(cut + 1), false, true);
}
else {
return isRational(s);
}
}
private boolean isRational(String s) {
int cut = s.indexOf(".");
if (cut != -1) {
String first = s.substring(0, cut);
String second = s.substring(cut + 1);
return (isInteger(first, true, true) && isInteger(second, false, false)) || (isInteger(first, false, true) && isInteger(second, true, false));
}
else {
return isInteger(s, false, true);
}
}
private boolean isInteger(String s, boolean canBeEmpty, boolean canHaveSign) {
if (s.length() == 0) {
return canBeEmpty;
}
if (s.charAt(0) == '-' || s.charAt(0) == '+') {
if (canHaveSign == true) {
s = s.substring(1);
}
else {
return false;
}
}
if (s.length() == 0) {
return canBeEmpty;
}
for (int i = 0; i < s.length(); i ++) {
char c = s.charAt(i);
if (c < '0' || c > '9') {
return false;
}
}
return true;
}
}
``````