LC8. 字符串转换整数 (atoi)：DFA有限状态机

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题

DFA

class Automaton {string state = "start";unordered_map<string, vector<string>> table = {{"start", {"start", "signed", "in_number", "end"}},{"signed", {"end", "end", "in_number", "end"}},{"in_number", {"end", "end", "in_number", "end"}},{"end", {"end", "end", "end", "end"}}};int get_col(char c) {if (isspace(c)) return 0;if (c == '+' or c == '-') return 1;if (isdigit(c)) return 2;return 3;}
public:int sign = 1;long long ans = 0;void get(char c) {state = table[state][get_col(c)];if (state == "in_number") {ans = ans * 10 + c - '0';ans = sign == 1 ? min(ans, (long long)INT_MAX) : min(ans, -(long long)INT_MIN);}else if (state == "signed")sign = c == '+' ? 1 : -1;}
};class Solution {
public:int myAtoi(string str) {Automaton automaton;for (char c : str)automaton.get(c);return automaton.sign * automaton.ans;}
};

经典测试：

"20000000000000000000"  // 超过long long，所以不能直接掉包stoll(s)

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