[topcoder]SmartWordToy

广度搜索BFS，要用Queue。还不是很熟，这道题帮助理清一些思绪了。其实这道题是求最短路径，所以BFS遇到第一个就可以返回了，所以后面有些现有大小和历史大小的判断可以省却。

过程中拿数组存step还是很有用的。其他的解法中我看到有把四位char编码返回整数的a*26*26*26+b*26*26+c*26+d，很不错，本质就是26进制的数。

import java.util.*;



public class SmartWordToy

{

	public int minPresses(String start, String finish, String[] forbid) {

		int[][][][] step = new int[26][26][26][26];

		int[][][][] forb = new int[26][26][26][26];

		for (int a = 0; a < 26; a++)

		for (int b = 0; b < 26; b++)

		for (int c = 0; c < 26; c++)

		for (int d = 0; d < 26; d++)

		{

			step[a][b][c][d] = -1;

			forb[a][b][c][d] = 0;

		}

		

		for (int i = 0; i < forbid.length; i++) {

			String[] lines = forbid[i].split(" ");

			for (int a = 0; a < lines[0].length(); a++) {

				for (int b = 0; b < lines[1].length(); b++) {

					for (int c = 0; c < lines[2].length(); c++) {

						for (int d = 0; d < lines[3].length(); d++) {

							forb[lines[0].charAt(a)-'a'][lines[1].charAt(b)-'a'][lines[2].charAt(c)-'a'][lines[3].charAt(d)-'a'] = 1;

						}

					}

				}

			}

		}

		

		LinkedList<Word> queue = new LinkedList<Word>();

		Word sw = new Word(start.charAt(0), start.charAt(1), start.charAt(2), start.charAt(3));

		step[sw.a-'a'][sw.b-'a'][sw.c-'a'][sw.d-'a'] = 0;

		queue.offer(sw);

		

		Word fw = new Word(finish.charAt(0), finish.charAt(1), finish.charAt(2), finish.charAt(3));



		while (queue.size() != 0) {

			Word w = queue.poll();

			int cur_step = step[w.a-'a'][w.b-'a'][w.c-'a'][w.d-'a'];

			if (w.a == fw.a && w.b == fw.b && w.c == fw.c && w.d == fw.d) return cur_step;

			

			Word tmp = new Word();

			tmp.a = next(w.a); tmp.b = w.b; tmp.c = w.c; tmp.d = w.d;

			int tmp_step = step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'];

			if (forb[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] == 0 && (tmp_step == -1 || tmp_step > cur_step+1)) {

				step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] = cur_step + 1;

				queue.offer(tmp);

			}

			tmp = new Word();

			tmp.a = prev(w.a); tmp.b = w.b; tmp.c = w.c; tmp.d = w.d;

			tmp_step = step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'];

			if (forb[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] == 0 && (tmp_step == -1 || tmp_step > cur_step+1)) {

				step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] = cur_step + 1;

				queue.offer(tmp);

			}

			tmp = new Word();

			tmp.a = w.a; tmp.b = next(w.b); tmp.c = w.c; tmp.d = w.d;

			tmp_step = step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'];

			if (forb[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] == 0 && (tmp_step == -1 || tmp_step > cur_step+1)) {

				step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] = cur_step + 1;

				queue.offer(tmp);

			}

			tmp = new Word();

			tmp.a = w.a; tmp.b = prev(w.b); tmp.c = w.c; tmp.d = w.d;

			tmp_step = step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'];

			if (forb[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] == 0 && (tmp_step == -1 || tmp_step > cur_step+1)) {

				step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] = cur_step + 1;

				queue.offer(tmp);

			}

			tmp = new Word();

			tmp.a = w.a; tmp.b = w.b; tmp.c = next(w.c); tmp.d = w.d;

			tmp_step = step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'];

			if (forb[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] == 0 && (tmp_step == -1 || tmp_step > cur_step+1)) {

				step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] = cur_step + 1;

				queue.offer(tmp);

			}

			tmp = new Word();

			tmp.a = w.a; tmp.b = w.b; tmp.c = prev(w.c); tmp.d = w.d;

			tmp_step = step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'];

			if (forb[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] == 0 && (tmp_step == -1 || tmp_step > cur_step+1)) {

				step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] = cur_step + 1;

				queue.offer(tmp);

			}

			tmp = new Word();

			tmp.a = w.a; tmp.b = w.b; tmp.c = w.c; tmp.d = next(w.d);

			tmp_step = step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'];

			if (forb[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] == 0 && (tmp_step == -1 || tmp_step > cur_step+1)) {

				step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] = cur_step + 1;

				queue.offer(tmp);

			}

			tmp = new Word();

			tmp.a = w.a; tmp.b = w.b; tmp.c = w.c; tmp.d = prev(w.d);

			tmp_step = step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'];

			if (forb[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] == 0 && (tmp_step == -1 || tmp_step > cur_step+1)) {

				step[tmp.a-'a'][tmp.b-'a'][tmp.c-'a'][tmp.d-'a'] = cur_step + 1;

				queue.offer(tmp);

			}

		}

		return step[finish.charAt(0)-'a'][finish.charAt(1)-'a'][finish.charAt(2)-'a'][finish.charAt(3)-'a'];

	}

	

	private char next(char c) {

		if (c == 'z') return 'a';

		else return (char)(c+1);

	}

	

	private char prev(char c) {

		if (c == 'a') return 'z';

		else return (char)(c-1);

	}

}



class Word

{

	char a;

	char b;

	char c;

	char d;

	

	public Word(char _a, char _b, char _c, char _d) {

		a = _a; b = _b; c = _c; d = _d;

	}

	

	public Word() {}

}