POJ1013解题报告

重点是枚举法，即从12个硬币中假设某个硬币为假，并设它重/轻。然后判断是否与题中所给的条件矛盾，如果不矛盾，则这个硬币为假硬币。（需注意的是，如果某次比较时，天平两边只放了一个硬币，且结果为up/down,那么其中一定一个硬币是假的，那么这两个硬币就一定要先比较）。

代码如下：

import java.util.ArrayList; import java.util.Scanner; public class Main { char[] never=new char[12]; int top=-1; //菜鸟代码，POJ1013 public char getChar(int i) { char[] mychar={'A','B','C','D','E','F','G','H','I','J','K','L'}; return mychar[i]; } public int getInt(char c) { int chn=0; switch(c) { case 'A':chn=0;break; case 'B':chn=1;break; case 'C':chn=2;break; case 'D':chn=3;break; case 'E':chn=4;break; case 'F':chn=5;break; case 'G':chn=6;break; case 'H':chn=7;break; case 'I':chn=8;break; case 'J':chn=9;break; case 'K':chn=10;break; case 'L':chn=11;break; } return chn; } //Judge public boolean judge(String[] result,ArrayList<char[]> list,int i,int tag) { boolean signal=true; char suspectcoin=getChar(i); //认为第i个硬币轻了 if(tag==0) { for(int k1=0;k1<3;k1++) { char[] c1=list.get(2*k1); char[] c2=list.get(2*k1+1); //System.out.println(c1.length); if(result[k1].equals("even")) { for(int m1=0;m1<c1.length;m1++) { if(c1[m1]==suspectcoin||c2[m1]==suspectcoin) { return false; } } } else if(result[k1].equals("up")) { for(int m1=0;m1<c1.length;m1++) { if(c1[m1]==suspectcoin) { return false; } } } else if(result[k1].equals("down")) { for(int m1=0;m1<c1.length;m1++) { if(c2[m1]==suspectcoin) { return false; } } } } } else if(tag==1) { for(int k1=0;k1<3;k1++) { char[] c1=list.get(2*k1); char[] c2=list.get(2*k1+1); if(result[k1].equals("even")) { for(int m1=0;m1<c1.length;m1++) { if(c1[m1]==suspectcoin||c2[m1]==suspectcoin) { return false; } } } else if(result[k1].equals("down")) { for(int m1=0;m1<c1.length;m1++) { if(c1[m1]==suspectcoin) { return false; } } } else if(result[k1].equals("up")) { for(int m1=0;m1<c1.length;m1++) { if(c2[m1]==suspectcoin) { return false; } } } } } return signal; } //有没有硬币没有出现过 public boolean neverexit(int n,ArrayList<char[]> list) { boolean tag=true; for(int i=0;i<list.size();i++) { char[] coin=list.get(i); for(int j=0;j<coin.length;j++) { if(coin[j]==getChar(n)) { return false; } } } return tag; } //获得输入 public void getInput() { String n; Scanner scan=new Scanner(System.in); n=scan.nextLine(); while(scan.hasNext()) { String[] result=new String[3]; ArrayList<char[]> list=new ArrayList<char[]>(); for(int i=0;i<3;i++) { String s1=scan.nextLine(); //System.out.println(s1); String[] s2=s1.split(" "); //System.out.println(s2[0].length()); char[] c1=s2[0].toCharArray(); char[] c2=s2[1].toCharArray(); list.add(c1); list.add(c2); result[i]=s2[2]; } boolean mytag=true; //是否有up,down且每边只有一个数据的，如果有，那么假的硬币就在其中 boolean mytag2=true; for(int i=0;i<3&&mytag2;i++) { if(result[i].equals("up")||result[i].equals("down")) { char[] c1=list.get(2*i); char[] c2=list.get(2*i+1); if(c1.length==1) { int i1=getInt(c1[0]); int i2=getInt(c2[0]); if(judge(result,list,i1,0)) { System.out.println(getChar(i1)+" is the counterfeit coin and it is light."); mytag2=false; //continue; } else if (judge(result, list, i1, 1)) { System.out.println(getChar(i1)+" is the counterfeit coin and it is heavy."); mytag2=false; //continue; } else if (judge(result, list, i2, 0)) { System.out.println(getChar(i2)+" is the counterfeit coin and it is light."); mytag2=false; //continue; } else if (judge(result, list, i2, 1)) { System.out.println(getChar(i2)+" is the counterfeit coin and it is heavy."); mytag2=false; //continue; } } } } //分别枚举进行判断 for(int i=0;i<12&&mytag&&mytag2;i++) { if(this.neverexit(i, list)) { never[++top]=getChar(i); continue; } if(judge(result,list,i,0)) { System.out.println(getChar(i)+" is the counterfeit coin and it is light."); mytag=false; continue; } else if(judge(result, list, i, 1)) { System.out.println(getChar(i)+" is the counterfeit coin and it is heavy."); mytag=false; continue; } } //System.out.println("end program"); } } public static void main(String[] args) { Main m=new Main(); m.getInput(); } }