Leetcode8. 字符串转换整数 (atoi)

 

> 简洁易懂讲清原理，讲不清你来打我~

输入字符串，输出整数

> 有限状态机

简单的思路
建立状态转换图和状态转换表，哈希表存储状态转移表的行索引和新的状态，通过行索引的原始状态和列索引的字符获得新的状态状态，遇到数字放入结果的个位

准确的定义
state是当前的状态
table是状态转换表
positive是当前计算结果的绝对值
c是当前的字符
isPositive是结果是否为正数

```cpp
class Solution {
public:
int myAtoi(string str) {
for (char c : str)change(c);
if(isPositive)return positive;
else return -positive;
}
void change(char c) {
state = table[state][getCol(c)];
if (state == "in_number") {
positive = positive * 10 + c - '0';
positive = isPositive? min(positive, (long long)INT_MAX) : min(positive, -(long long)INT_MIN);
}
else if (state == "signed"&&c=='-')isPositive=false;
}
int getCol(char c) {
if (isspace(c)) return 0;
if (c == '+' || c == '-') return 1;
if (isdigit(c)) return 2;
return 3;
}
private:
string state = "start";
int isPositive = 1;
long long positive = 0;
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"}}
};
};
```

踩过的坑

```cpp
long long positive = 0;

positive = isPositive? min(positive, (long long)INT_MAX) : min(positive, -(long long)INT_MIN);

else if (state == "signed"&&c=='-')isPositive=false;
```

 

 

 

 

 

 

 

 

 

 

 

 

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