后缀树和前缀树

给你一个很长的字符串 s，和一堆短字符串 T = {t1, t2, ...}。 设计一个高效的算法，确定T 里的每个字符串是不是 s 的子串。

思路：先对字符串s构建一个后缀树，然后看看t1，t2...，是不是s的一个后缀的前缀。

构建后缀树和查找后缀树的前缀都可以用递归的思路来解决。

具体代码如下：

public class SuffixTree {
	SuffixTreeNode root = new SuffixTreeNode();
	public SuffixTree(String s) {
		for (int i = 0; i < s.length(); i++) {
			String suffix = s.substring(i);
			root.insertString(suffix, i);
		}
	}

	public ArrayList<Integer> getIndexes(String s) {
		return root.getIndexes(s);
	}
}

public class SuffixTreeNode {
	HashMap<Character, SuffixTreeNode> children = new
	HashMap<Character, SuffixTreeNode>();
	char value;
	ArrayList<Integer> indexes = new ArrayList<Integer>();
	public SuffixTreeNode() { }

	public void insertString(String s, int index) {
		indexes.add(index);
		if (s != null && s.length() > 0) {
			value = s.charAt(0);
			SuffixTreeNode child = null;
			if (children.containsKey(value)) {
				child = children.get(value);
			} else {
				child = new SuffixTreeNode();
				children.put(value, child);
			}
			String remainder = s.substring(1);
			child.insertString(remainder, index);
		}
	}

	public ArrayList<Integer> getIndexes(String s) {
		if (s == null || s.length() == 0) {
			return indexes;
		} else {
			char first = s.charAt(0);
			if (children.containsKey(first)) {
				String remainder = s.substring(1);
				return children.get(first).getIndexes(remainder);
			}
		}
		return null;
	}
}

public class Question {
	public static void main(String[] args) {
		String testString = “mississippi”;
		String[] stringList = {“is”, “sip”, “hi”, “sis”};
		SuffixTree tree = new SuffixTree(testString);
		for (String s : stringList) {
			ArrayList<Integer> list = tree.getIndexes(s);
			if (list != null) {
				System.out.println(s + “: “ + list.toString());
			}
		}
	}
}