问题描述

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.

原题链接：https://leetcode.com/problems/string-to-integer-atoi/

Analysis

public int myAtoi(String str) {

    if(str == null || str.length() == 0){

        return 0;

    }

    char[] chs = str.trim().toCharArray();

    int isPositive = 1, index = 0;

    if(chs[0] == '-'){

        isPositive = -1;

        index = 1;

    }

    if(chs[0] == '+'){

        isPositive = 1;

        index = 1;

    }

    long res = 0;

    for(; index < chs.length; index++){

        if(chs[index] <  '0' || chs[index] > '9' ){

            return (int)res;

        }

        res = res * 10 + isPositive * (chs[index] - '0');

        if(res > Integer.MAX_VALUE){

            return Integer.MAX_VALUE;

        }

        if(res < Integer.MIN_VALUE){

            return Integer.MIN_VALUE;

        }

    }

    return (int)res;

}