LeetCode：剑指 Offer 20. 表示数值的字符串（C语言）
题目描述：
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。
解答：
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,
STATE_ILLEGAL
};
enum CharType {
CHAR_NUMBER,
CHAR_EXP,
CHAR_POINT,
CHAR_SIGN,
CHAR_SPACE,
CHAR_ILLEGAL
};
enum CharType toCharType(char ch) {
if (ch >= '0' && ch <= '9') {
return CHAR_NUMBER;
} else if (ch == 'e' || ch == 'E') {
return CHAR_EXP;
} else if (ch == '.') {
return CHAR_POINT;
} else if (ch == '+' || ch == '-') {
return CHAR_SIGN;
} else if (ch == ' ') {
return CHAR_SPACE;
} else {
return CHAR_ILLEGAL;
}
}
enum State transfer(enum State st, enum CharType typ) {
switch (st) {
case STATE_INITIAL: {
switch (typ) {
case CHAR_SPACE:
return STATE_INITIAL;
case CHAR_NUMBER:
return STATE_INTEGER;
case CHAR_POINT:
return STATE_POINT_WITHOUT_INT;
case CHAR_SIGN:
return STATE_INT_SIGN;
default:
return STATE_ILLEGAL;
}
}
case STATE_INT_SIGN: {
switch (typ) {
case CHAR_NUMBER:
return STATE_INTEGER;
case CHAR_POINT:
return STATE_POINT_WITHOUT_INT;
default:
return STATE_ILLEGAL;
}
}
case STATE_INTEGER: {
switch (typ) {
case CHAR_NUMBER:
return STATE_INTEGER;
case CHAR_EXP:
return STATE_EXP;
case CHAR_POINT:
return STATE_POINT;
case CHAR_SPACE:
return STATE_END;
default:
return STATE_ILLEGAL;
}
}
case STATE_POINT: {
switch (typ) {
case CHAR_NUMBER:
return STATE_FRACTION;
case CHAR_EXP:
return STATE_EXP;
case CHAR_SPACE:
return STATE_END;
default:
return STATE_ILLEGAL;
}
}
case STATE_POINT_WITHOUT_INT: {
switch (typ) {
case CHAR_NUMBER:
return STATE_FRACTION;
default:
return STATE_ILLEGAL;
}
}
case STATE_FRACTION: {
switch (typ) {
case CHAR_NUMBER:
return STATE_FRACTION;
case CHAR_EXP:
return STATE_EXP;
case CHAR_SPACE:
return STATE_END;
default:
return STATE_ILLEGAL;
}
}
case STATE_EXP: {
switch (typ) {
case CHAR_NUMBER:
return STATE_EXP_NUMBER;
case CHAR_SIGN:
return STATE_EXP_SIGN;
default:
return STATE_ILLEGAL;
}
}
case STATE_EXP_SIGN: {
switch (typ) {
case CHAR_NUMBER:
return STATE_EXP_NUMBER;
default:
return STATE_ILLEGAL;
}
}
case STATE_EXP_NUMBER: {
switch (typ) {
case CHAR_NUMBER:
return STATE_EXP_NUMBER;
case CHAR_SPACE:
return STATE_END;
default:
return STATE_ILLEGAL;
}
}
case STATE_END: {
switch (typ) {
case CHAR_SPACE:
return STATE_END;
default:
return STATE_ILLEGAL;
}
}
default:
return STATE_ILLEGAL;
}
}
bool isNumber(char* s) {
int len = strlen(s);
enum State st = STATE_INITIAL;
for (int i = 0; i < len; i++) {
enum CharType typ = toCharType(s[i]);
enum State nextState = transfer(st, typ);
if (nextState == STATE_ILLEGAL) return false;
st = nextState;
}
return st == STATE_INTEGER || st == STATE_POINT || st == STATE_FRACTION || st == STATE_EXP_NUMBER || st == STATE_END;
}
运行结果：
Notes：
参考文档：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/