LeetCode 8 String to Integer (atoi)

题目

Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

Update (2015-02-10):
The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button to reset your code definition.

解法

本来以为只是简单的数字字符转换，后来根据报错发现还要考虑空格和正负号等问题。

class Solution {public:    int myAtoi(string str) {        int length = str.length();        if (length == 0)  return 0;        int left = 0, right = length - 1;        while(str[left] == ' ' && left < length) left++;        while(str[right] == ' ' && right > 0) right --;        int flag = 1;        if (str[left] == '+') {left++;}        else if (str[left] == '-') {left++; flag = -1;}        long ans = 0;        for(int i = left; i <= right; i++) {            if(str[i] < '0' || str[i] > '9') break;            ans = ans * 10 + str[i] - '0';              if(ans > INT_MAX && flag == 1) return INT_MAX;              else if(ans > INT_MAX && flag == -1) return INT_MIN;        }        return ans*flag;      }};