编程珠玑

在第四步中，我们看到，使用排序好的String[] 要比 ArrayList<String> 查找时候快速的多，因为ArrayList<String>的查找复杂度O(n)，而排序好的String[]查找复杂度O(1)。

但是我们还是过量依赖String，这个对象本身效率就不高，于是我们需要换成更底层的原始类型进行优化：

package test;

import static util.PrintUtil.print;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

public class Test {
	static String[] keys = {"办证", "气枪出售", "裸聊", "裸表演", "土枪卖"};
	static String tContent = "再办证顶";
	static ArrayList<String> first = new ArrayList<String>();
	static String[] sortFirst;
	static char[] charFirst;
	static HashMap<String, ArrayList<String>> map = new HashMap<String, ArrayList<String>>();
	static HashMap<String, String[]> sortMap = new HashMap<String, String[]>();
	static HashMap<String, char[]> charMap = new HashMap<String, char[]>();
	static {
		ArrayList<String> temp;
		String key, value;
		int length;
		for (String k : keys) {
			if (!first.contains(k.substring(0, 1))) {
				first.add(k.substring(0, 1));
			}
			length = k.length();
			for (int i = 1; i < length; i ++) {
				key = k.substring(0, i);
				value = k.substring(i, i + 1);
				if (i == 1 && !first.contains(key)) {
					first.add(key);
				}
				
				// 有，添加
				if (map.containsKey(key)) {
					if (!map.get(key).contains(value)) {
						map.get(key).add(value);
					}
				}
				// 没有添加
				else {
					temp = new ArrayList<String>();
					temp.add(value);
					map.put(key, temp);
				}
			}
		}
		sortFirst = first.toArray(new String[first.size()]);
		Arrays.sort(sortFirst); // 排序
		
		charFirst = new char[first.size()];
		for (int i = 0; i < charFirst.length; i ++) {
			charFirst[i] = first.get(i).charAt(0);
		}
		Arrays.sort(charFirst); // 排序
		
		String[] sortValue;
		ArrayList<String> v;
		Map.Entry<String, ArrayList<String>> entry;
		Iterator<Entry<String, ArrayList<String>>> iter = map.entrySet().iterator();
		while (iter.hasNext()) {
			entry = (Map.Entry<String, ArrayList<String>>) iter.next();
			v = (ArrayList<String>)entry.getValue();
			sortValue = v.toArray(new String[v.size()]);
			Arrays.sort(sortValue); // 排序
			sortMap.put(entry.getKey(), sortValue);
		}
		
		char[] charValue;
		iter = map.entrySet().iterator();
		while (iter.hasNext()) {
			entry = (Map.Entry<String, ArrayList<String>>) iter.next();
			v = (ArrayList<String>)entry.getValue();
			charValue = new char[v.size()];
			for (int i = 0; i < charValue.length; i ++) {
				charValue[i] = v.get(i).charAt(0);
			}
			Arrays.sort(charValue); // 排序
			charMap.put(entry.getKey(), charValue);
		}
	}
	
	/**
	 * 快速实现的方法
	 */
	public final static String test1(String content) {
		for (String k : keys) {
			if (content.indexOf(k) > -1)
				return k;
		}
		return null;
	}
	
	/**
	 * 优化一
	 */
	public final static String test2(String content) {
		boolean bFirst = false;
		int length = content.length();
		for (int i = 0; i < length; i ++) {
			if (first.contains(content.substring(i, i + 1))) {
				bFirst = true;
				break;
			}
		}
		return bFirst ? test1(content) : null;
	}
	
	/**
	 * 优化二
	 */
	public final static String test3(String content) {
		String r = null, f, g, c = content;
		ArrayList<String> temps;
		int length = c.length();
		tag : for (int i = 0; i < length - 1; i++) {
			f = c.substring(i, i + 1);
			if (first.contains(f)) {
				for (int j = i + 1; j < length; j++) {
					f = c.substring(i, j);
					g = c.substring(j, j + 1);
					temps = map.get(f);
					if (temps == null) { // 找到了
						print("ok");
						r = f;
						break tag;
					}
					if (temps.contains(g)) {
						if (j == length - 1) {
							print("find!");
							r = c.substring(i, j + 1);
							break tag;
						}
					} else { // 没有找到了
						break;
					}
				}
			}
		}
		return r;
	}
	
	/**
	 * 优化三
	 */
	public final static String test4(String content) {
		String r = null, f, g, c = content;
		String[] temps;
		int length = c.length();
		tag : for (int i = 0; i < length - 1; i++) {
			f = c.substring(i, i + 1);
			// 二分查找
			if (Arrays.binarySearch(sortFirst, f) > -1) {
				for (int j = i + 1; j < length; j++) {
					f = c.substring(i, j);
					g = c.substring(j, j + 1);
					temps = sortMap.get(f);
					if (temps == null) { // 找到了
						print("ok");
						r = f;
						break tag;
					}
					// 二分查找
					if (Arrays.binarySearch(temps, g) > -1) {
						if (j == length - 1) {
							print("find!");
							r = c.substring(i, j + 1);
							break tag;
						}
					} else { // 没有找到了
						break;
					}
				}
			}
		}
		return r;
	}
	
	/**
	 * 优化四
	 */
	public final static String test5(String content) {
		String r = null, f, c = content;
		char g;
		char[] temps;
		int length = c.length();
		tag : for (int i = 0; i < length - 1; i++) {
			g = c.charAt(i);
			// 二分查找
			if (Arrays.binarySearch(charFirst, g) > -1) {
				for (int j = i + 1; j < length; j++) {
					f = c.substring(i, j);
					g = c.charAt(j);
					temps = charMap.get(f);
					if (temps == null) { // 找到了
						print("ok");
						r = f;
						break tag;
					}
					// 二分查找
					if (Arrays.binarySearch(temps, g) > -1) {
						if (j == length - 1) {
							print("find!");
							r = c.substring(i, j + 1);
							break tag;
						}
					} else { // 没有找到了
						break;
					}
				}
			}
		}
		return r;
	}
	
	public static void main(String[] args) {
		long time1 = System.currentTimeMillis();
		print(test5(tContent));
		print("test5 time:" + (System.currentTimeMillis() - time1));
	}
}

来源：oschina

链接：https://my.oschina.net/u/113867/blog/32386