LeetCode-in-Java

745. Prefix and Suffix Search

Hard

Design a special dictionary with some words that searchs the words in it by a prefix and a suffix.

Implement the WordFilter class:

• WordFilter(string[] words) Initializes the object with the words in the dictionary.
• f(string prefix, string suffix) Returns the index of the word in the dictionary, which has the prefix prefix and the suffix suffix. If there is more than one valid index, return the largest of them. If there is no such word in the dictionary, return -1.

Example 1:

Input

[“WordFilter”, “f”]

[[[“apple”]], [“a”, “e”]]

Output: [null, 0]

Explanation:

WordFilter wordFilter = new WordFilter(["apple"]); 
wordFilter.f("a", "e"); // return 0, because the word at index 0 has prefix = "a" and suffix = 'e".

Constraints:

• 1 <= words.length <= 15000
• 1 <= words[i].length <= 10
• 1 <= prefix.length, suffix.length <= 10
• words[i], prefix and suffix consist of lower-case English letters only.
• At most 15000 calls will be made to the function f.

Solution

public class WordFilter {
    private static class TrieNode {
        TrieNode[] children;
        int weight;

        TrieNode() {
            this.children = new TrieNode[27];
            this.weight = 0;
        }
    }

    private TrieNode root = new TrieNode();

    public WordFilter(String[] words) {
        for (int i = 0; i < words.length; i++) {
            String s = words[i];
            for (int j = 0; j < s.length(); j++) {
                insert(s.substring(j) + '{' + s, i);
            }
        }
    }

    public void insert(String wd, int weight) {
        TrieNode node = root;
        for (char ch : wd.toCharArray()) {
            if (node.children[ch - 'a'] == null) {
                node.children[ch - 'a'] = new TrieNode();
            }
            node = node.children[ch - 'a'];
            node.weight = weight;
        }
    }

    public int f(String prefix, String suffix) {
        return startsWith(suffix + '{' + prefix);
    }

    public int startsWith(String pref) {
        TrieNode node = root;
        for (char ch : pref.toCharArray()) {
            if (node.children[ch - 'a'] == null) {
                return -1;
            }
            node = node.children[ch - 'a'];
        }
        return node.weight;
    }
}

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