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    这道题虽然我用ifelse 做出来了，但是正儿八经的正统算法还是需要自动机来完成的，
    包括电梯问题。

    我的代码

    1.  public static void main(String[] args) {
    2.         String s = "   1  11   ";
    3.         System.out.println("===" +s.trim()+ "===");
    4.         String ss = "-1E-16";
    5.         System.out.println(isNumber(ss));
    6.     }
    7.     public static boolean isNumber(String s) {
    8.         if(s == null  || s.length() == 0) return false;
    9.         boolean res = process(s.trim().toCharArray());
    10.         return res;
    11.     }
    12.     public static boolean process(char[] chs){
    13.         if(chs.length ==0) return false;
    14.         if( chs.length ==1  && (chs[0] < '0' || chs[0]>'9') )return false;
    15.         int e = -1;
    16.         for(int i = 0; i<chs.length; i++){
    17.             if(chs[i] =='e' || chs[i] =='E'){
    18.                 e = i;
    19.                 break;
    20.             }
    21.         }
    22.         boolean res;
    23.         if(e != -1){
    24.             res = pointNum(chs, 0, e-1) && eNum(chs, e, chs.length-1);
    25.         }else {
    26.             res = pointNum(chs, 0, chs.length-1);
    27.         }
    28.         return res;
    29.     }
    31.     public static boolean posNum(char[] chs, int i , int j){
    32.         if(i==j && (chs[i]<'0' || chs[i] >'9' )) return false;
    33.         if(chs[i] != '+' && (chs[i]<'0' || chs[i]>'9')) {
    34.             return false;
    35.         }
    36.         else {
    37.             for(int index = i+1; index <=j; index ++){
    38.                 if(chs[index] > '9' || chs[index]<'0') return false;
    39.             }
    40.         }
    41.        return true;
    42.     }
    43.     public static boolean negNum(char[] chs, int i, int j){
    44.         if(i==j && (chs[i]<'0' || chs[i] >'9' )) return false;
    45.         if(chs[i] != '-' && (chs[i]<'0' || chs[i]>'9')) {
    46.             return false;
    47.         }
    48.         else {
    49.             for(int index = i+1; index <= j ; index ++){
    50.                 if(chs[index] > '9' || chs[index]<'0') return false;
    51.             }
    52.         }
    53.         return true;
    54.     }
    55.     public static boolean pointNum(char[] chs, int i , int j){
    56.         if(i==j && (chs[i]<'0' || chs[i] >'9' )) return false;
    57.         if(j-i ==1 && chs[j] =='.' && (chs[i]<'0' || chs[i] > '9')) return false; 
    58.         boolean point = false;
    59.         if(chs[i] !='.' && chs[i] !='+' && chs[i]!='-' &&( chs[i]<'0' || chs[i]>'9')){
    60.             return false;
    61.         }
    62.         if(chs[i] == '.'){
    63.             point = true;
    64.         }
    65.         for(int index =i+1; index<=j; index++){
    66.             if(!point  && chs[index] != '.' && ( chs[index] <'0' || chs[index]> '9')){
    67.                 return false;
    68.             }else if(point && chs[index] =='.'){
    69.                 return false;
    70.             }else if(!point && chs[index] == '.') {
    71.                 point = true;
    72.             }else if( chs[index] <'0' || chs[index]> '9'){
    73.                 return false;
    74.             }
    75.         }
    76.         return true;
    77.     }
    79.     /**i 表示 e首次出现的位置*/
    80.     public static boolean eNum(char[] chs, int i, int j){
    81.         boolean hasE = false;
    82.         if(i +1 == chs.length) return false;
    83.         return posNum(chs,i+1,j) || negNum(chs, i+1, j );
    84.     }

    官方题解：

    1. class Solution {
    2.     public boolean isNumber(String s) {
    3.         Map<State, Map<CharType, State>> transfer = new HashMap<State, Map<CharType, State>>();
    4.         Map<CharType, State> initialMap = new HashMap<CharType, State>() {{
    5.             put(CharType.CHAR_SPACE, State.STATE_INITIAL);
    6.             put(CharType.CHAR_NUMBER, State.STATE_INTEGER);
    7.             put(CharType.CHAR_POINT, State.STATE_POINT_WITHOUT_INT);
    8.             put(CharType.CHAR_SIGN, State.STATE_INT_SIGN);
    9.         }};
    10.         transfer.put(State.STATE_INITIAL, initialMap);
    11.         Map<CharType, State> intSignMap = new HashMap<CharType, State>() {{
    12.             put(CharType.CHAR_NUMBER, State.STATE_INTEGER);
    13.             put(CharType.CHAR_POINT, State.STATE_POINT_WITHOUT_INT);
    14.         }};
    15.         transfer.put(State.STATE_INT_SIGN, intSignMap);
    16.         Map<CharType, State> integerMap = new HashMap<CharType, State>() {{
    17.             put(CharType.CHAR_NUMBER, State.STATE_INTEGER);
    18.             put(CharType.CHAR_EXP, State.STATE_EXP);
    19.             put(CharType.CHAR_POINT, State.STATE_POINT);
    20.             put(CharType.CHAR_SPACE, State.STATE_END);
    21.         }};
    22.         transfer.put(State.STATE_INTEGER, integerMap);
    23.         Map<CharType, State> pointMap = new HashMap<CharType, State>() {{
    24.             put(CharType.CHAR_NUMBER, State.STATE_FRACTION);
    25.             put(CharType.CHAR_EXP, State.STATE_EXP);
    26.             put(CharType.CHAR_SPACE, State.STATE_END);
    27.         }};
    28.         transfer.put(State.STATE_POINT, pointMap);
    29.         Map<CharType, State> pointWithoutIntMap = new HashMap<CharType, State>() {{
    30.             put(CharType.CHAR_NUMBER, State.STATE_FRACTION);
    31.         }};
    32.         transfer.put(State.STATE_POINT_WITHOUT_INT, pointWithoutIntMap);
    33.         Map<CharType, State> fractionMap = new HashMap<CharType, State>() {{
    34.             put(CharType.CHAR_NUMBER, State.STATE_FRACTION);
    35.             put(CharType.CHAR_EXP, State.STATE_EXP);
    36.             put(CharType.CHAR_SPACE, State.STATE_END);
    37.         }};
    38.         transfer.put(State.STATE_FRACTION, fractionMap);
    39.         Map<CharType, State> expMap = new HashMap<CharType, State>() {{
    40.             put(CharType.CHAR_NUMBER, State.STATE_EXP_NUMBER);
    41.             put(CharType.CHAR_SIGN, State.STATE_EXP_SIGN);
    42.         }};
    43.         transfer.put(State.STATE_EXP, expMap);
    44.         Map<CharType, State> expSignMap = new HashMap<CharType, State>() {{
    45.             put(CharType.CHAR_NUMBER, State.STATE_EXP_NUMBER);
    46.         }};
    47.         transfer.put(State.STATE_EXP_SIGN, expSignMap);
    48.         Map<CharType, State> expNumberMap = new HashMap<CharType, State>() {{
    49.             put(CharType.CHAR_NUMBER, State.STATE_EXP_NUMBER);
    50.             put(CharType.CHAR_SPACE, State.STATE_END);
    51.         }};
    52.         transfer.put(State.STATE_EXP_NUMBER, expNumberMap);
    53.         Map<CharType, State> endMap = new HashMap<CharType, State>() {{
    54.             put(CharType.CHAR_SPACE, State.STATE_END);
    55.         }};
    56.         transfer.put(State.STATE_END, endMap);
    58.         int length = s.length();
    59.         State state = State.STATE_INITIAL;
    61.         for (int i = 0; i < length; i++) {
    62.             CharType type = toCharType(s.charAt(i));
    63.             if (!transfer.get(state).containsKey(type)) {
    64.                 return false;
    65.             } else {
    66.                 state = transfer.get(state).get(type);
    67.             }
    68.         }
    69.         return state == State.STATE_INTEGER || state == State.STATE_POINT || state == State.STATE_FRACTION || state == State.STATE_EXP_NUMBER || state == State.STATE_END;
    70.     }
    72.     public CharType toCharType(char ch) {
    73.         if (ch >= '0' && ch <= '9') {
    74.             return CharType.CHAR_NUMBER;
    75.         } else if (ch == 'e' || ch == 'E') {
    76.             return CharType.CHAR_EXP;
    77.         } else if (ch == '.') {
    78.             return CharType.CHAR_POINT;
    79.         } else if (ch == '+' || ch == '-') {
    80.             return CharType.CHAR_SIGN;
    81.         } else if (ch == ' ') {
    82.             return CharType.CHAR_SPACE;
    83.         } else {
    84.             return CharType.CHAR_ILLEGAL;
    85.         }
    86.     }
    88.     enum State {
    89.         STATE_INITIAL,
    90.         STATE_INT_SIGN,
    91.         STATE_INTEGER,
    92.         STATE_POINT,
    93.         STATE_POINT_WITHOUT_INT,
    94.         STATE_FRACTION,
    95.         STATE_EXP,
    96.         STATE_EXP_SIGN,
    97.         STATE_EXP_NUMBER,
    98.         STATE_END
    99.     }
    101.     enum CharType {
    102.         CHAR_NUMBER,
    103.         CHAR_EXP,
    104.         CHAR_POINT,
    105.         CHAR_SIGN,
    106.         CHAR_SPACE,
    107.         CHAR_ILLEGAL
    108.     }
    109. }
    111. 作者：LeetCode-Solution
    112. 链接：https://leetcode-cn.com/problems/biao-shi-shu-zhi-de-zi-fu-chuan-lcof/solution/biao-shi-shu-zhi-de-zi-fu-chuan-by-leetcode-soluti/
    113. 来源：力扣（LeetCode）
    114. 著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。