玛雅人的密码（BFS）

宽度优先搜索，这道题还需要再好好吃透。

package 机试;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashSet;
import java.util.LinkedList;

public class D3_23_4 {
	public static class Data {
		String str;
		int time;

		public Data(String str, int time) {
			this.str = str;
			this.time = time;
		}
	}
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		String line;
		while((line=br.readLine())!=null)
		{
			int n=Integer.valueOf(line);
			String str=br.readLine();
			System.out.println(BFS(n,str));
		}
		br.close();
	}

	private static int BFS(int n, String str) {
		// TODO Auto-generated method stub
		LinkedList <Data> list=new LinkedList<>();
		HashSet<String> set = new HashSet<>();
		if(isContain(str))
		{
			return 0;
		}
		else
		{
			list.add(new Data(str,0));
			set.add(str);
		}
		Data cur;
		String next;
		int times;
		while(!list.isEmpty())
		{
			cur=list.poll();
			times=cur.time;
			for(int i=0;i<n-1;i++)
			{
				if (cur.str.charAt(i) != cur.str.charAt(i + 1)) {
					next = swapString(i, cur.str);
					if (isContain(next)) {
						return times + 1;
					}
					if(!set.contains(next))
					{
						set.add(next);
						list.add(new Data(next,times+1));}
				}
			}
		}

		return -1;

	}

	private static String swapString(int i, String str) {
		// TODO Auto-generated method stub
		char[] chs = str.toCharArray();
		char c = chs[i];
		chs[i] = chs[i + 1];
		chs[i + 1] = c;
		return new String(chs);
	}

	private static boolean isContain(String str) {
		// TODO Auto-generated method stub
		char[] chs = str.toCharArray();
		for (int i = 0; i + 3 < str.length(); i++) {
			if (chs[i] == '2' && chs[i + 1] == '0' && chs[i + 2] == '1' && chs[i + 3] == '2') {
				return true;
			}
		}
		return false;
	}



}