2013
11-10

# POJ 2105 IP Address [解题报告] Java

Suppose you are reading byte streams from any device, representing IP addresses. Your task is to convert a 32 characters long sequence of ’1s’ and ’0s’ (bits) to a dotted decimal format. A dotted decimal format for an IP address is form by grouping 8 bits at a time and converting the binary representation to decimal representation. Any 8 bits is a valid part of an IP address. To convert binary numbers to decimal numbers remember that both are positional numerical systems, where the first 8 positions of the binary systems are:
27   26  25  24  23   22  21  20
128 64  32  16  8   4   2   1 

The input will have a number N (1<=N<=9) in its first line representing the number of streams to convert. N lines will follow.

The output must have N lines with a doted decimal IP address. A dotted decimal IP address is formed by grouping 8 bit at the time and converting the binary representation to decimal representation.

4
00000000000000000000000000000000
00000011100000001111111111111111
11001011100001001110010110000000
01010000000100000000000000000001 

0.0.0.0
3.128.255.255
203.132.229.128
80.16.0.1


import java.util.*;

public class Main {

public static void main(String[] args) {
Scanner cin = new Scanner(System.in);

int num = Integer.valueOf(cin.nextLine()).intValue();

for(int i = 0; i < num; i++)
{
String str, temp;
int a,b,c,d = 0;
StringBuffer sb = new StringBuffer();

str = cin.nextLine();
temp = str.substring(0, 8);
sb.append(convert(temp));
sb.append('.');
temp = str.substring(8, 16);
sb.append(convert(temp));
sb.append('.');
temp = str.substring(16, 24);
sb.append(convert(temp));
sb.append('.');
temp = str.substring(24);
sb.append(convert(temp));

System.out.println(sb.toString());
}

}

private static int convert(String str)
{
int value = 0;
if(str.charAt(0) == '1')
value += 128;
if(str.charAt(1) == '1')
value += 64;
if(str.charAt(2) == '1')
value += 32;
if(str.charAt(3) == '1')
value += 16;
if(str.charAt(4) == '1')
value += 8;
if(str.charAt(5) == '1')
value += 4;
if(str.charAt(6) == '1')
value += 2;
if(str.charAt(7) == '1')
value += 1;

return value;
}

}

1. “再把所有不和该节点相邻的节点着相同的颜色”，程序中没有进行不和该节点相邻的其他节点是否相邻进行判断。再说求出来的也不一样是颜色数最少的

2. 第一题是不是可以这样想，生了n孩子的家庭等价于n个家庭各生了一个1个孩子，这样最后男女的比例还是1:1