LeetCode-面试题20-表示数值的字符串

class Solution {
    public boolean isNumber(String s) {
        if(s==null||s.length()==0)
            return false;
        boolean isNum = false;
        boolean isDot = false;
        boolean isE = false;
        char[] str = s.trim().toCharArray();
        for(int i = 0;i < str.length;i++){
            if(str[i]>='0'&&str[i]<='9'){
                isNum = true;
            }
            else if('.'==str[i]){
                // .的前面不能有.或者E
                if(isDot||isE)
                    return false;
                isDot = true;
            }
            else if(str[i]=='e'||str[i]=='E'){
                // e或E的前面不能有e/E，只能是数字
                if(isE||isNum==false)
                    return false;
                isE = true;
                // 越过e之后必须要有数字，重置isNum，记录后面是不是有数字出现
                // 如果e是最后一位，则这个数字不合法
                isNum = false;
            }
            else if(str[i]=='+'||str[i]=='-'){
                // 只有i=0或者e/E前面出现正负号的时候才合法，不然就是非法
                if(i!=0&&str[i-1]!='e'&&str[i-1]!='E')
                    return false;
            }
            else{ // 其他非法情况
                return false;
            }
        }
        return isNum;
    }
}

class Solution:
    def __init__(self):
        self.p = 0

    def isNumber(self, s: str) -> bool:
        s = s.strip()
        if not s: return False
        numeric = self.scanInteger(s)
        if self.p > len(s)-1:
            return numeric
        if self.p < len(s) and s[self.p] == '.':
            self.p +=1
            if self.p > len(s)-1:
                return numeric
            numeric = self.scanUnsignedIntergers(s) or numeric
        if self.p < len(s) and s[self.p] in ['e','E']:
            self.p +=1
            if self.p > len(s)-1:
                return False
            numeric = numeric and self.scanInteger(s)
        if self.p < len(s):
            return False
        return numeric
    
    def scanInteger(self,s):
        if s[self.p] in ['+','-']:
            self.p +=1
        return self.scanUnsignedIntergers(s)
    
    def scanUnsignedIntergers(self,s):
        pre = self.p
        while(self.p < len(s) and s[self.p]>='0' and s[self.p]<='9'):
            self.p +=1
        return self.p>pre