_65.java

package com.fishercoder.solutions;

/**
 * 65. Valid Number
 *
 * 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.
 */

public class _65 {
  /**credit: https://discuss.leetcode.com/topic/9490/clear-java-solution-with-ifs*/
  public static class Solution1 {
    public boolean isNumber(String s) {
      s = s.trim();

      boolean pointSeen = false;
      boolean eSeen = false;
      boolean numberSeen = false;
      boolean numberAfterE = true;
      for (int i = 0; i < s.length(); i++) {
        if ('0' <= s.charAt(i) && s.charAt(i) <= '9') {
          numberSeen = true;
          numberAfterE = true;
        } else if (s.charAt(i) == '.') {
          if (eSeen || pointSeen) {
            return false;
          }
          pointSeen = true;
        } else if (s.charAt(i) == 'e') {
          if (eSeen || !numberSeen) {
            return false;
          }
          numberAfterE = false;
          eSeen = true;
        } else if (s.charAt(i) == '-' || s.charAt(i) == '+') {
          if (i != 0 && s.charAt(i - 1) != 'e') {
            return false;
          }
        } else {
          return false;
        }
      }

      return numberSeen && numberAfterE;
    }
  }

  public static class Solution2 {
    /** credit: https://discuss.leetcode.com/topic/2973/java-solution-with-one-line */
    public boolean isNumber(String s) {
      return s.matches("(\\s*)[+-]?((\\.[0-9]+)|([0-9]+(\\.[0-9]*)?))(e[+-]?[0-9]+)?(\\s*)");
    }
  }
}