[LeetCode] 65. Valid Number Java

Posted 2020-10-20 BrookLearnData

题目：

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.

Update (2015-02-10):
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题意及分析：判断一个字符串是否能转化为合法的数字，主要注意至多只能一个小数点和e，e后面不能有小数点第一位或最后一位可以为小数点，+/-只能出现在第一位或者e后面的第一位。

代码：

class Solution {
    public boolean isNumber(String s) {     //判断一个字符串是不是合法的数字
        s = s.trim();
        boolean pointSeen = false;
        boolean eSeen = false;
        boolean isNumber = false;

        for(int i=0;i<s.length();i++){
            char temp = s.charAt(i);
            if(temp>=‘0‘ && temp<=‘9‘){
                isNumber = true;
            }else if(temp == ‘.‘){
                if(eSeen || pointSeen)
                    return false;
                pointSeen = true;
            }else if(temp == ‘e‘){
                if(eSeen || !isNumber)
                    return false;
                eSeen = true;
                isNumber = false;
            }else if(temp == ‘+‘ || temp==‘-‘){     //只能在首位或者isNumber后面为+/-
                if(i!=0 && s.charAt(i-1)!=‘e‘ )
                    return false;
                isNumber = false;
            }else
                return false;
        }

        return isNumber;
    }

}