241. String to Integer

描述

• Given a string, convert it to an integer. * You may assume the string is a valid
• integer number that can be presented by a * signed 32bit integer (-231 ~ 231-1).

样例

给出 "123", 返回 123.

public class Solution {
    /**
     * @param str: A string
     * @return: An integer
     */
    public int stringToInteger(String str) {
        // write your code here

        return Integer.parseInt(str);
        //return Integer.valueOf(str);

    }
}

public class Solution {
    /**
     * @param str: A string
     * @return: An integer
     */
    public int stringToInteger(String str) {
        // write your code here
        int integer = 0;
        int negative = 0;//1为true是负数，0为false是正数

        if (str.charAt(0) == '-'){
            negative = 1;
        }

        for (int i = negative; i < str.length(); i++){
            integer = integer * 10 + str.charAt(i)-'0';
            //假设str=1000
            //i=0 integer=0*10+1=1;
            //i=1 integer=1*10+0=10;
            //i=2 integer=10*10+0=100;
            //i=3 integer=100*10+0=1000;
        }

        if (negative == 1){
            integer = -integer;
        }
        return integer;
    }
}