【题目】*剑指 Offer 20. 表示数值的字符串
请实现一个函数用来判断字符串是否表示数值（包括整数和小数）。例如，字符串"+100"、“5e2”、"-123"、“3.1416”、"-1E-16"、“0123"都表示数值，但"12e”、“1a3.14”、“1.2.3”、"±5"及"12e+5.4"都不是。
【解题思路1】确定有限状态自动机
class Solution {
public boolean isNumber(String s) {
Map<State, Map<CharType, State>> transfer = new HashMap<State, Map<CharType, State>>();
Map<CharType, State> initialMap = new HashMap<CharType, State>() {
{
put(CharType.CHAR_SPACE, State.STATE_INITIAL);
put(CharType.CHAR_NUMBER, State.STATE_INTEGER);
put(CharType.CHAR_POINT, State.STATE_POINT_WITHOUT_INT);
put(CharType.CHAR_SIGN, State.STATE_INT_SIGN);
}};
transfer.put(State.STATE_INITIAL, initialMap);
Map<CharType, State> intSignMap = new HashMap<CharType, State>() {
{
put(CharType.CHAR_NUMBER, State.STATE_INTEGER);
put(CharType.CHAR_POINT, State.STATE_POINT_WITHOUT_INT);
}};
transfer.put(State.STATE_INT_SIGN, intSignMap);
Map<CharType, State> integerMap = new HashMap<CharType, State>() {
{
put(CharType.CHAR_NUMBER, State.STATE_INTEGER);
put(CharType.CHAR_EXP, State.STATE_EXP);
put(CharType.CHAR_POINT, State.STATE_POINT);
put(CharType.CHAR_SPACE, State.STATE_END);
}};
transfer.put(State.STATE_INTEGER, integerMap);
Map<CharType, State> pointMap = new HashMap<CharType, State>() {
{
put(CharType.CHAR_NUMBER, State.STATE_FRACTION);
put(CharType.CHAR_EXP, State.STATE_EXP);
put(CharType.CHAR_SPACE, State.STATE_END);
}};
transfer.put(State.STATE_POINT, pointMap);
Map<CharType, State> pointWithoutIntMap = new HashMap<CharType, State>() {
{
put(CharType.CHAR_NUMBER, State.STATE_FRACTION);
}};
transfer.put(State.STATE_POINT_WITHOUT_INT, pointWithoutIntMap);
Map<CharType, State> fractionMap = new HashMap<CharType, State>() {
{
put(CharType.CHAR_NUMBER, State.STATE_FRACTION);
put(CharType.CHAR_EXP, State.STATE_EXP);
put(CharType.CHAR_SPACE, State.STATE_END);
}};
transfer.put(State.STATE_FRACTION, fractionMap);
Map<CharType, State> expMap = new HashMap<CharType, State>() {
{
put(CharType.CHAR_NUMBER, State.STATE_EXP_NUMBER);
put(CharType.CHAR_SIGN, State.STATE_EXP_SIGN);
}};
transfer.put(State.STATE_EXP, expMap);
Map<CharType, State> expSignMap = new HashMap<CharType, State>() {
{
put(CharType.CHAR_NUMBER, State.STATE_EXP_NUMBER);
}};
transfer.put(State.STATE_EXP_SIGN, expSignMap);
Map<CharType, State> expNumberMap = new HashMap<CharType, State>() {
{
put(CharType.CHAR_NUMBER, State.STATE_EXP_NUMBER);
put(CharType.CHAR_SPACE, State.STATE_END);
}};
transfer.put(State.STATE_EXP_NUMBER, expNumberMap);
Map<CharType, State> endMap = new HashMap<CharType, State>() {
{
put(CharType.CHAR_SPACE, State.STATE_END);
}};
transfer.put(State.STATE_END, endMap);
int length = s.length();
State state = State.STATE_INITIAL;
for (int i = 0; i < length; i++) {
CharType type = toCharType(s.charAt(i));
if (!transfer.get(state).containsKey(type)) {
return false;
} else {
state = transfer.get(state).get(type);
}
}
return state == State.STATE_INTEGER || state == State.STATE_POINT || state == State.STATE_FRACTION || state == State.STATE_EXP_NUMBER || state == State.STATE_END;
}
public CharType toCharType(char ch) {
if (ch >= '0' && ch <= '9') {
return CharType.CHAR_NUMBER;
} else if (ch == 'e' || ch == 'E') {
return CharType.CHAR_EXP;
} else if (ch == '.') {
return CharType.CHAR_POINT;
} else if (ch == '+' || ch == '-') {
return CharType.CHAR_SIGN;
} else if (ch == ' ') {
return CharType.CHAR_SPACE;
} else {
return CharType.CHAR_ILLEGAL;
}
}
enum State {
STATE_INITIAL,
STATE_INT_SIGN,
STATE_INTEGER,
STATE_POINT,
STATE_POINT_WITHOUT_INT,
STATE_FRACTION,
STATE_EXP,
STATE_EXP_SIGN,
STATE_EXP_NUMBER,
STATE_END,
}
enum CharType {
CHAR_NUMBER,
CHAR_EXP,
CHAR_POINT,
CHAR_SIGN,
CHAR_SPACE,
CHAR_ILLEGAL,
}
}