leetcode 日经贴，Cpp code -String to Integer (atoi)

String to Integer (atoi)

class Solution {
public:
    string trim(string s) {
        int n = s.length();
        if (n == 0) return s;
        int st = 0, ed = n - 1;
        while (s[st] == ' ') {
            ++st;
        }
        while (s[ed] == ' ') {
            --ed;
        }
        if (st > ed) return "";
        return s.substr(st, ed - st + 1);
    }
    int myAtoi(string str) {
        str = trim(str);
        int n = str.length();
        int neg = 1;
        int st = 0;
        if (str[0] == '-') {
            st++;
            neg = -1;
        } else if (str[0] == '+') {
            st++;
        }
        long long val = 0;
        while (st < n) {
            if (str[st] < '0' || str[st] > '9') {
                break;
            }
            val = val * 10 + (str[st++] - '0');
            if (val > INT_MAX || val < INT_MIN){
                break;
            }
        }
        val *= neg;
        if (val > INT_MAX) {
            val = INT_MAX;
        } else if (val < INT_MIN) {
            val = INT_MIN;
        }
        return val;
    }
};