表示数值的字符串-剑指Offer

表示数值的字符串

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。

思路

1. 数值的结构是‘+/-‘ + ‘整数‘ + ‘.‘ + ‘整数‘ + ‘E/e‘ + ‘+/-‘ + ‘整数‘
2. 按结构一个个的匹配，如果用if语句可以只匹配一次

代码

public class Solution {
    public boolean isNumeric(char[] str) {
        if (str == null || str.length == 0) {
            return false;
        }
        int point = 0;
        int length = str.length;
        if (str[0] == ‘-‘ || str[0] == ‘+‘) {
            point++;
        }
        boolean result = true;
        while (point < length && str[point] >= ‘0‘ && str[point] <= ‘9‘) {
            point++;
        }
        if (point < length) {
            if (str[point] == ‘.‘) {
                point++;
                while (point < length && str[point] >= ‘0‘ && str[point] <= ‘9‘) {
                    point++;
                }
                if (point == length) {
                    return true;
                }
                if (str[point] == ‘e‘ || str[point] == ‘E‘) {
                    result = isE(str, point);
                }else {
	                return false;
	            }
            } else if (str[point] == ‘e‘ || str[point] == ‘E‘) {
                result = isE(str, point);
            } else {
                result = false;
            }
        }
        return result;
    }
    public boolean isE(char[] str, int start) {
        if (str[start] != ‘e‘ && str[start] != ‘E‘) {
            return false;
        }
        start++;
        if (start == str.length) {
	        	return false;
	        }
        if (str[start] == ‘+‘ || str[start] == ‘-‘) {
            start++;
        }
        if (start == str.length) {
            return false;
        }
        while (start < str.length && str[start] <= ‘9‘ && str[start] >= ‘0‘) {
            start++;
        }
        if (start == str.length) {
            return true;
        } else {
            return false;
        }

    }
}