unordered_map

        unordered_map Containers , The literal translation is " disorder map Containers " It means . So-called “ disorder ”, refer to unordered_map Containers don't look like map Sort the stored data like a container . let me put it another way ,unordered_map Container and map Containers are only a little different , namely map The data stored in the container is orderly , and unordered_map The container is unordered .

         In particular ,unordered_map Container and map The container is the same , Pair with key value （pair type ） In the form of data storage , The keys of each stored key value pair are different from each other and cannot be modified . But because of unordered_map The bottom layer of the container adopts the hash table storage structure , The structure itself does not have the function of sorting data , Therefore, this container will not sort the stored key value pairs by itself .

Example

function  myAtoi(string s) The algorithm is as follows ：

Read in strings and discard useless leading spaces
Check the next character （ Suppose you haven't reached the end of the character yet ） Positive or negative , Read the character （ If there is ）. Determine whether the final result is negative or positive . If neither exists , Suppose the result is positive .
Read in the next character , Until you reach the next non numeric character or the end of the input . The rest of the string will be ignored .
Convert the numbers read in the previous steps into integers （ namely ,"123" -> 123, "0032" -> 32）. If you don't read in the numbers , Then the integer is 0 . Change the symbol if necessary （ From step 2 Start ）.
If the number of integers exceeds 32 Bit signed integer range [−231,  231 − 1] , You need to truncate this integer , Keep it in this range . say concretely , Less than −231 The integer of should be fixed to −231 , Greater than 231 − 1 The integer of should be fixed to 231 − 1 .
Returns an integer as the final result .
Be careful ：

The white space character in this question only includes the space character ' ' .
Except for the leading space or the rest of the string after the number , Do not ignore Any other character .

source ： Power button （LeetCode）
link ：https://leetcode-cn.com/problems/string-to-integer-atoi
Copyright belongs to the network . For commercial reprint, please contact the official authority , Non-commercial reprint please indicate the source .

Explain

class Automaton {
    string state = "start";// Status word 
    unordered_map<string, vector<string>> table = {// Definition unordered_map（ Pay attention to key value Yes , among value by string Vector of type ）
        {"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) {// Choose different values according to different characters , namely map The corresponding subscript in the vector in 
        if (isspace(c)) return 0;// Judge whether it is a space 
        if (c == '+' or c == '-') return 1;
        if (isdigit(c)) return 2;// Is it a number 
        return 3;
    }
public:
    int sign = 1;
    long long ans = 0;

    void get(char c) {
        state = table[state][get_col(c)];//state The corresponding key ,get_col(c) Corresponding value vector coordinates 
        if (state == "in_number") {
            ans = ans * 10 + c - '0';
            ans = sign == 1 ? min(ans, (long long)INT_MAX) : min(ans, -(long long)INT_MIN);// Judge whether it is beyond the scope of expression 
        }
        else if (state == "signed")// Select symbol 
            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;
    }
};

author ：LeetCode-Solution
link ：https://leetcode-cn.com/problems/string-to-integer-atoi/solution/zi-fu-chuan-zhuan-huan-zheng-shu-atoi-by-leetcode-/
source ： Power button （LeetCode）
The copyright belongs to the author . Commercial reprint please contact the author for authorization , Non-commercial reprint please indicate the source .