面试题—小算法20题

1、IP转换成整数及整数转换成IP

Java实现：

package com.mian.demo;

public class IpToInt {
    public static void main(String[] args) {
        String ip="192.168.12.90";
        int ipInt=ipToInt(ip);
        System.out.println(ipInt);
        String ipStr=intToIp(ipInt);
        System.out.println(ipStr);
    }
    private static String intToIp(int ip){
        StringBuilder sb=new StringBuilder();
        for(int i=3;i>=0;--i){
            int ipa=(ip>>(8*i))&(0xff);
            System.out.print(ipa+" ");
            sb.append(String.valueOf(ipa)+".");
        }
        return new String(sb).substring(0,sb.length()-1);
    }
    private static int ipToInt(String ip){
        int res=0;
        String[] arr=ip.split("\\.");
        for(int i=0;i<arr.length;++i){
            int ipa=Integer.parseInt(arr[i]);
            System.out.print(ipa+" ");
            res=(res<<8)|ipa;//用+也可以,但是位运算更快
        }
        return res;
    }
}

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