目錄

題目描述：

演算法實現：

題目描述：

Validate if a given string can be interpreted as a decimal number.

Some examples:

"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true
" -90e3   " => true
" 1e" => false
"e3" => false
" 6e-1" => true
" 99e2.5 " => false
"53.5e93" => true
" --6 " => false
"-+3" => false
"95a54e53" => false
 

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one. However, here is a list of characters that can be in a valid decimal number:

• Numbers 0-9
• Exponent - "e"
• Positive/negative sign - "+"/"-"
• Decimal point - "."

Of course, the context of these characters also matters in the input.

Update (2015-02-10): The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button to reset your code definition.

演算法實現：

總體來說比較簡單，只需要將正確的幾種形式弄清即可

（+/-）number(.number)(e number)

需要注意的是有一些情況需要根據除錯結果進行調整，比如空格的處理，比如，"1."，".2"都被認為是對的等

具體演算法中，博主維護了一個i來掃描整個字串，如下

class Solution {
public:
    //跳過空格
    void jumpblack(string s, int &i){
        while(s[i] == ' ')i ++;
    }
    //跳過數字序列，如果有數字序列返回true，否則返回false
    bool jumpdigits(string s, int &i){
        int j = i;
        while(s[i] != '\0' && s[i] >= '0' && s[i] <= '9')
            i ++;
        if(i > j)return true;
        else return false;
            
    }
    //判斷e後面的序列合不合乎要求
    bool judge_after_E(string s, int &i){
        if(s[i] == '\0')return false;
        if(s[i] == '+' || s[i] == '-') i ++;
        if(s[i] == '\0')return false;
        bool flag = jumpdigits(s, i);
        jumpblack(s, i);
        return s[i] == '\0' && flag;
    }
    bool isNumber(string s) {
        if(s.empty())return false;
        int i = 0;
        jumpblack(s, i);
        if(s[i] == '+' || s[i] == '-') i ++;
        if(s[i] == '\0')return false;
        bool flag = jumpdigits(s, i);
        if(s[i] != '\0'){
            if(s[i] == ' '){
                jumpblack(s, i);
                if(s[i] == '\0')return flag;
                else return false;
            }
            else if(s[i] == '.'){
                i ++;
                bool flag1 = jumpdigits(s, i);
                if(s[i] == ' ' || s[i] == '\0'){
                    jumpblack(s, i);
                    if(s[i] == '\0')return (flag || flag1);
                    else return false;
                }
                else if((flag1||flag) && s[i] == 'e')return judge_after_E(s, ++i);
                else return false;
            }
            else if(flag && s[i] == 'e')return judge_after_E(s, ++ i);
            else return false;
        }
        else return true;
    }

};