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Leetcode: Valid Number
Validate if a given string is numeric.
Some examples:"0" => true" 0.1 " => true"abc" => false"1 a" => false"2e10" => true
Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.
分析：这道题用Deterministic Finite Automata解，逻辑清晰，代码简洁，关键在于正确画出DFA，几个应该注意的case是".1", "1."都是有效的，但"."是无效的。DFA如下：
C++代码如下：
class Solution {public: bool isNumber(const char *s) { enum InputType{ INVALID, SPACE, SIGN,//+,- DIGIT, DOT, EXP }; int transitionMatrix[][6] = { -1, 0, 1, 2, 3, -1,//next state of S0 -1, -1, -1, 2, 3, -1,//next state of S1 -1, 8, -1, 2, 4, 5,//next state of S2 -1, -1, -1, 4, -1, -1,//next state of S3 -1, 8, -1, 4, -1, 5,//next state of S4 -1, -1, 6, 7, -1, -1,//next state of S5 -1, -1, -1, 7, -1, -1,//next state of S6 -1, 8, -1, 7, -1, -1,//next state of S7 -1, 8, -1, -1, -1, -1//next state of S8 }; int state = 0; while(*s != ‘\0‘){ InputType itype = INVALID; if(*s == ‘ ‘) itype = SPACE; else if(*s == ‘+‘ || *s == ‘-‘) itype = SIGN; else if(isdigit(*s)) itype = DIGIT; else if(*s == ‘.‘) itype = DOT; else if(*s == ‘e‘ || *s == ‘E‘) itype = EXP; state = transitionMatrix[state][itype]; if(state == -1) return false; s++; } return state == 2 || state == 4 || state == 7 || state == 8; }};
Leetcode: Valid Number
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