题目描述
验证给定的字符串是否为数字。 例如: “0” => true ” 0.1 ” => true “abc” => false “1 a” => false “2e10” => true 说明: 我们有意将问题陈述地比较模糊。在实现代码之前，你应当事先思考所有可能的情况。
思路：
主要是考虑各种可能的情况，如”+.” ” 123” 等等。
代码
class Solution {
public boolean isNumber(String s) {
boolean ret =
false;
if(s ==
null || s.equals(
"")){
return ret;
}
if(
"+.".equals(s.trim()))
return false;
if(
"-.".equals(s.trim()))
return false;
char[] str2char = s.toCharArray();
int start =
0;
for(
int i =
0; i < str2char.length;++i){
if(str2char[i] ==
' ') {
start ++;
continue;
}
break;
}
int end = str2char.length;
for(
int i = str2char.length -
1 ; i >=
0 ;-- i){
if(str2char[i] ==
' ') {
end --;
continue;
}
break;
}
if(start == str2char.length)
return ret;
int countE =
0;
int countDot =
0;
boolean hasE =
false;
boolean hasDot =
false;
int countP =
0;
int countC =
0;
int posE =
0;
int posDot =
0;
int posC =
0;
int posP =
0;
for(
int i = start; i < end; ++ i){
if(i == start && (str2char[i] >
'9' || str2char[i] <
'0') && str2char[i] !=
'-' && str2char[i] !=
'+' && str2char[i] !=
'.')
return ret;
if(i == start && (str2char[i] ==
'-' || str2char[i] ==
'+')){
continue;
}
if((str2char[i] <=
'9' && str2char[i] >=
'0') || str2char[i] ==
'e' || str2char[i] ==
'E' || str2char[i] ==
'.' ||
str2char[i] ==
'+' || str2char[i] ==
'-'){
if(countE <=
1 && countDot <=
1 && str2char[i] <=
'9' && str2char[i] >=
'0'){
continue;
}
if(str2char[i] ==
'e' || str2char[i] ==
'E'){
hasE =
true;
countE ++;
posE = i;
continue;
}
if(str2char[i] ==
'.'){
hasDot =
true;
posDot = i;
countDot ++;
continue;
}
if(str2char[i] ==
'+'){
countP ++;
posP = i;
continue;
}
if(str2char[i] ==
'-'){
countC ++;
posC = i;
continue;
}
}
if(str2char[i] >
'9' || str2char[i] <
'0' ){
return ret;
}
}
if(countE >
1)
return ret;
if(countDot >
1)
return ret;
if(countP >
1){
return ret;
}
if(countC >
1){
return ret;
}
if((countP ==
1 || countC ==
1) && !hasE )
return ret;
if(countP ==
1 && posP == end -
1)
return ret;
if(countC ==
1 && posC == end -
1)
return ret;
if(countP ==
1 && hasE && posE == posP -
1 && posP != end -
1)
return true;
if(countC ==
1 && hasE && posE == posC -
1 && posC != end -
1)
return true;
if(hasE && hasDot && posE < posDot)
return ret;
if(hasE && (posE == end -
1 || str2char[posE +
1] >
'9' || str2char[posE +
1] <
'0' ||
(hasDot && posDot==start && posE == posDot +
1) ||
(posE-
1 < start || str2char[posE -
1] ==
'+' || str2char[posE -
1] ==
'-') ))
return ret;
if(hasDot && ((posDot -
1) >= start &&
((str2char[posDot -
1] >
'9' || str2char[posDot -
1] <
'0') &&
(str2char[posDot -
1] !=
'+' && str2char[posDot -
1] !=
'-') )))
return ret;
if(end - start ==
1 && hasDot)
return ret;
return true;
}
}
