algorithm-class/体系学习班/class08/Code02_Trie.java

package class08;

import java.util.HashMap;

public class Code02_Trie {

	// 测试链接 : https://leetcode.cn/problems/implement-trie-ii-prefix-tree/
	// 提交Trie类可以直接通过
	// 原来代码是对的，但是既然找到了直接测试的链接，那就直接测吧
	// 这个链接上要求实现的功能和课上讲的完全一样
	// 该前缀树的路用哈希表实现
	class Trie {

		class Node {
			public int pass;
			public int end;
			public HashMap<Integer, Node> nexts;

			public Node() {
				pass = 0;
				end = 0;
				nexts = new HashMap<>();
			}
		}

		private Node root;

		public Trie() {
			root = new Node();
		}

		public void insert(String word) {
			if (word == null) {
				return;
			}
			char[] chs = word.toCharArray();
			Node node = root;
			node.pass++;
			int index = 0;
			for (int i = 0; i < chs.length; i++) {
				index = (int) chs[i];
				if (!node.nexts.containsKey(index)) {
					node.nexts.put(index, new Node());
				}
				node = node.nexts.get(index);
				node.pass++;
			}
			node.end++;
		}

		public void erase(String word) {
			if (countWordsEqualTo(word) != 0) {
				char[] chs = word.toCharArray();
				Node node = root;
				node.pass--;
				int index = 0;
				for (int i = 0; i < chs.length; i++) {
					index = (int) chs[i];
					if (--node.nexts.get(index).pass == 0) {
						node.nexts.remove(index);
						return;
					}
					node = node.nexts.get(index);
				}
				node.end--;
			}
		}

		public int countWordsEqualTo(String word) {
			if (word == null) {
				return 0;
			}
			char[] chs = word.toCharArray();
			Node node = root;
			int index = 0;
			for (int i = 0; i < chs.length; i++) {
				index = (int) chs[i];
				if (!node.nexts.containsKey(index)) {
					return 0;
				}
				node = node.nexts.get(index);
			}
			return node.end;
		}

		public int countWordsStartingWith(String pre) {
			if (pre == null) {
				return 0;
			}
			char[] chs = pre.toCharArray();
			Node node = root;
			int index = 0;
			for (int i = 0; i < chs.length; i++) {
				index = (int) chs[i];
				if (!node.nexts.containsKey(index)) {
					return 0;
				}
				node = node.nexts.get(index);
			}
			return node.pass;
		}
	}

}