题目描述
请实现一个函数用来判断字符串是否表示数值(包括整数和小数)。例如,字符串"+100","5e2","-123","3.1416"和"-1E-16"都表示数值。 但是"12e","1a3.14","1.2.3","+-5"和"12e+4.3"都不是。
题目链接:
package com.sunshine.OFFER66_SECOND; import org.junit.Test; public class A53_isNumeric { @Test public void test() { String number = "5e2"; String[] numbers = {"+100", "5e2", "-123", "3.1416", "-1E-16"}; for (String s : numbers) { boolean numeric = isNumeric2(s.toCharArray()); System.out.println(numeric); } System.out.println(); String[] numbers2 = {"12e", "1a3.14", "1.2.3", "+-5", "12e+4.3"}; for (String s : numbers2) { boolean numeric = isNumeric2(s.toCharArray()); System.out.println(numeric); } } public boolean isNumeric(char[] str) { int pm1 = 1; int pm2 = 1; boolean e = false; int point = -1; int a = 0; double b = 0; int c = 0; for (int i = 0; i < str.length; i++) { if (str[i] == '+') { if (i == 0) { pm1 = 1; } else if (i - 1 >= 0 && (str[i - 1] == 'e' || str[i - 1] == 'E')) { pm2 = 1; } else { return false; } } else if (str[i] == '-') { if (i == 0) { pm1 = -1; } else if (i - 1 >= 0 && (str[i - 1] == 'e' || str[i - 1] == 'E')) { pm2 = -1; } else { return false; } } else if (str[i] == 'e' || str[i] == 'E') { e = true; if (i == str.length - 1) { return false; } } else if (!e) { if (str[i] == '.') { if (point != -1) { return false; } point = i; } else if (point != -1) { if (str[i] >= '0' && str[i] <= '9') { a = a * 10 + str[i] - '0'; } else { return false; } } else { if (str[i] >= '0' && str[i] <= '9') { b += (str[i] - '0') * 1.0 / ((i - point) * 10); } else { return false; } } } else { if (str[i] >= '0' && str[i] <= '9') { c = c * 10 + str[i] - '0'; } else { return false; } } } return true; } //其他优解 public boolean isNumeric2(char[] str) { String string = String.valueOf(str); return string.matches("[\\+\\-]?\\d*(\\.\\d+)?([eE][\\+\\-]?\\d+)?"); } /** * [\\+\\-]? -> 正或负符号出现与否 * \\d* -> 整数部分是否出现,如-.34 或 +3.34均符合 * (\\.\\d+)? -> 如果出现小数点,那么小数点后面必须有数字; * 否则一起不出现 * ([eE][\\+\\-]?\\d+)? -> 如果存在指数部分,那么e或E肯定出现,+或-可以不出现, * 紧接着必须跟着整数;或者整个部分都不出现 */ }