Leetcode 65 Valid Number

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Examples of the first to observe, as well as the title character in answer to the prompt that can be included --valid

Find:

"+ -" either at the beginning or followed by e, only these two positions

"E", before and after must have a number, and not appeared before e

".", Appeared in front of e or not. ""

 

So we can use several flag

There have been digital representation before seenNum

E represents digital After seenNumAfterE

dot represents the appearance before too. ""

E represents occurred before e

 

Note that initialization of seenNumAfterE = true, because not necessarily contain e s, e again appears like it to false. Other flag are set to false

Finally, return seenNum && seenNumAfterE

 

 1 class Solution {
 2     public boolean isNumber(String s) {
 3         boolean seenNum = false, seenNumAfterE = true;
 4         boolean dot = false, e = false;
 5         s = s.trim(); //去掉首尾的空格
 6         int count = 0;
 7         for(char i : s.toCharArray()){
 8             if(i >= '0' && i <= '9'){
 9                 seenNum = true;
10                 seenNumAfterE = true;
11             }else if(i == '.'){
12                 if(e || dot)
13                     return false;
14                 dot = true;
15             }else if(i == 'e'){
16                 if(e || !seenNum)
17                     return false;
18                 seenNumAfterE = false;
19                 e = true;
20             }else if(i == '+' || i == '-'){
21                 if(count != 0 && s.charAt(count - 1) != 'e')
22                     return false;
23             }else
24                 return false;
25             
26             count++;
27         }
28         
29         return seenNum && seenNumAfterE;
30     }
31 }