链接：题目 思路与算法：有限状态自动机 题解代码:
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, } }